M416 Build Up


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I've been wanting a trailer for some time (5/6 years).. had been debating various options out there... was always leaning towards a Building Dinoot, but I have always thought the M416's looked so good behind a jeep. I wanted to be able to pull it with my YJ, or my JK so I didnt really want too massive a trailer. My plan was always a small gear trailer with a RTT mounted on top. I was close last year, as there was a good one within a 2 hr drive, but the seller wanted too much... I was randomly searching craigslist in February and found an M416 within driving distance (6hrs) that was reasonable. I'm in Denver, and I was able to break away an schedule pickup March 13. March 14 Colorado went into Covid Lockdown, so I picked it up in the nick of time! There was an m100 here in Denver on at the same time for about the same price, but I like the angled fenders better...

Here it is when I picked it up:

Between the fact it was a reasonable price, and that it was the flat fenders and basically the same color as my Jeep I had to do it! (My Jeep is kitted out in Jurassic World livery in case you're wondering about the stickers).

Plans: I'm putting a smittybilt XL on this, but I didn't want the high center of gravity for the rack, and I don't really think I need the annex room... So Remove the rack, make a hard cover, mount tent to that. Extend tongue slightly to clear tailgate, and use a multiaxis hitch (its 2" ball now). Trail tools. Gas/Water - Maybe just do inside... Other as need/wants dictate...

Starting off of course the lid is first, so I have been working on that over Covid isolation, Minimizing trips to hardware stores, and ordering parts online has probably slowed my progress, but you know.. trying to follow the stay at home guidance....

I don't have tools/welding gear, so I decided to go the wood cover route. I followed what guidance I could from Tventuring/dinoot on making a "plywood" cover. With the M416 measuring out at 49.25" x 74. 25" a standard 4x8 wouldn't cover the whole top without either 2 sheets and 1 seem, or multiple seams. Based on what I realized as I worked through this all I think well done seams, epoxied and coated, probably could have been fine.. but hindsight is 20/20. Instead I came up with a design that takes the angles of the m416 and mirrors them into the lid.

By using a 2x6 laid at a 45 degree angle, running it through my table saw 3 times to cut angles into it at the ends, and then 2x3 ribs, I could create the top and only need a single sheet of plywood in standard 4x8. Here is some of my math/drawings on how this works out:

The math here was made to align the size of the 2x6 to the 2x3 ribs (a 2x6 on angle is not long enough for 2x4 rib) . Really brushed off those geometry skills ;)

Here is the completed framework:

The 2x3s are end caps, and then ribs, I did it this way as I felt the connection would be better, and I didn't want seams in the front or rear. Here is a closeup of a corner (it looks like the 2x6 and 2x3 do not align, but it is a trick of the fact that dimensional lumber has rounded corners...

Next installed the plywood top:

I spaced the ribs so that when I mount the RTT, the bolts will go through the ribs, so I wasn't worried to much about thickness on the plywood, it wont hold any weight, and is really just a shell. So I used 1/4" plywood. I think this would be too thin unless you have plenty of ribs like I do. Even with 5 ribs + ends and sides, I almost thought I needed to go to 3/8. I was trying to minimize unnecessary weight. I was committed by this point though so I kept with it. I glued and screwed the plywood down, and started using various epoxies to finish the top.

I used 2 different epoxies: JBWeld - Wood Weld. I used this epoxy to fill/smooth out the countersunk screws. Very hard stuff once set. Sanding this down took some doing, and a few places I was almost going through the plywood veneer trying to get the epoxy to sand down.... It was a bit difficult to work with, as it was very thick & sticky, so spreading it over these screws was tricky. But I have no doubt it will fail long after the wood has issues. The second Wood Epoxy I used is a product called WoodEpox, its by Abatron. It is an indoor/outdoor wood filler epoxy. Its designed to fill holes/gaps in rotted wood. It is sandable and holds screws etc... This product is really light weight, mixing it was interesting since its not like a liquid its a putty, but a really light weight one. It was very dry as well. Once I figured out the best way to get it to stay where I wanted it, I liked it, but that took a bit of trial and error, since it was so dry it didn't exactly want to stay if you dragged your putty knife over it wrong. Once it was on it was great to shape/sand. So i really like that side of it.
In Progress:

The Yellow is the JBWeld, the Light tan is the Wood Epox. Here is the sanded look:

Since dimensional lumber isn't dried/finished like finish lumber, I went back over the 2x6 shown here with additional wood epox to minimize those imperfections.(not pictured)


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I am coating the top with Durabak Smooth. I coated the top with 3 layers of durabk on the outside, and 2 on the inside.

For Hinges, I needed to go around the M416's lip. I have seen a bunch of different options, but I ended up going with a heavy duty marine stainless steel offset hinge. Sea Dog Heavy Duty Offset hinge is how to find them online. This hinge is offset so I can attach it directly to the tub, and the offset sits around the lip.

The issue is Since I put an angle to my top, the longer 3rd screw doesn't align with the lid:

After Checking with the tventuring folks, on the hinges they used on plywood covers, I laid out 3 options, try to bend the leaf, cut it off, or use spacers. Considering I decided to use 4 of these hinges and they are thick, I decided to just cut them down. I painted the hinges black, and drilled out the hinge pin, and replaced it with a cap head bolt and nylock nuts so I can remove the top by taking out hinge pins instead of unscrewing the hinge leafs.

So Here is where I am today... I will be installing the latches and the gas springs hopefully soon, then the tent gets bolted on.

WOW, Nice job! There must be more than 1,000 M416 trailer build threads in here, yet you came up with an original solution that I don't remember seeing in here before. In the movie, "Find Forrester", Sean Connery says, "Well, you've taken something which was mine... ...and made it yours. Quite an accomplishment."


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Over the weekend I had a chance to finish off (for the most part) Phase I. SO Maybe I can go offgrid this weekend for the holiday weekend. NFS says all set facilities (campground, toilets, picnic areas( are closed, and no campfires, but dispersed camping is ok.

I still needed to take off the ball hitch, and length the tongue, so that was first up. Boy do I wish I had a drill press.... hand drilling 4, 1/2" holes in receiver tube was no fun.. and one of my holes was a bit off, guess the bit wandered some as I was drilling.... but some grinding with my Dremel fixed that up... When I removed the ball hitch, I took a look up the tube, and sure enough, this was a pintle someone had cut off and welded up 2" tube steel over. but man however they tapered the tube end down, was a clean job..... see pics.. The bolts for the ball the front one is in the pic, the back one is THROUGH the original cast intle bar... so I have no worries about this thing... I can only imagine what someone went through drilling the original cast pintle.... However it was done... based on the way it looks I have to figure someone who knew what they were doing did it.

With the Ball removed, I slid the receiver tube over this, and then sized so that I could jackknife the trailer, and open the tailgate. With the 24" receiver tube I had for this, I ended up with 7.5 inches over overlap on the existing tube, and it lengthened the overall tongue about 18 ish inches with the max coupler length.

Tailgate swings fully open, and if I jackknif the trailer to the driver side, nothing would hit to 90 degrees, on the passenger side, the new jack would hit the bumper shackle mount, unless I flip it up, in which case it would miss on that side as well. I lengthened the safety chains, but still need to length the trailer wiring.

I mounted the tent directly to the top I made, it screws into 3 of my cross members, so It isn't going anywhere. WOW the top is heavy now. I had planned for this, and lift struts had brackets installed, and just needed to be added. I went with some lift struts that were "camper lift struts" from amazon, that were 80lbs each... so theoretically 160lbs total.... they wont hold the top up on their own, but they do make it so my wife can lift the top without help.... Still working on a lid support for when open. (Or I could get stronger struts, if i can find right size/rating ones)

And here it is in I guess phase I complete form:

50 fiver

Very nice, reminds me of my trailer, my tongue extension is very much like yours, where someone bolted 3 inch tubing after cutting the original lunette. I just bolted on a new longer 3x3 tube to it. I really like the lid, very nice, gave me some ideas.
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Last weekend, Sat Morning, I finished up the last bits and pieces. I completed the wiring, and then we did a 1 night shakedown camp to the national forest. For the wiring, at one point the military wiring had been cut off, and the junction box removed. (My understanding is there should have been a junction box at the front of the frame). The wiring at this point was soldered to some 2 sets of speaker wire, which then fed a 6 prong round pin style connector, and then someone had a 6 pin round to 4 flat adaptor. So I took off all the extensions and rewired taking out all the speaker wire and such so the original trailer wiring is intact from the front of the frame to the lights, and then new 4 strand heavy jacket trailer wiring goes from there up to the new 4 prong flat connector. As I was doing all this, I discovered the rear license plate light (which is using the original Black-Out rear light housing) was never connected, and of course the lower 2 BO brake lights were not connected. The trailer had the original light covers replaced with the Gamma Goat full round red lamps, so I decided to make use of all the lights.

I added a junction box. The one I ordered from Amazon sounded right, but with the thick military wires and the heavy jacket 4 trailer I had to file out the connections to get the cables into the junction box, and the junction box was a tight fit. But should be watertight.... The junction box would likely be perfectly sized to splice together 2 standard outdoor extension cords... oh well.... With filing the fittings to accept the wire, and then over taping the connections it should still be watertight.

Since I was doing all this, I connected ALL the lights up. The standard m416 lights have 7 lights: 2 Tail light, left and Right Brake (your normal) PLUS 1 Black-Out tail and left and right BO brake/turn. Since I put in a new junction box, and was rewiring I hooked up the standard tail light and the BO light for tail lights and License plate light, then the left brake and the Left BO for brake turn, and the Right Brake and Right BO for brake and turn as well.. So now the whole round lens is being used not just the standard bulbs in the top portion.

With this complete, and my garage cleaned up my son, who has been chomping at the bit to get out camping, was all over me, so we left the house at 4:15 drove to the national forest and had it setup by 5:45.

EVerything worked good. Max coupler was so nice and quiet. Loving that, and it all trailed perfect. We had a few items we said would be nice to have additions to our gear, so I worked on those this week.

With me sticking with the stock military tires/wheels, I am working on painting mounting a 25mm ammo can (slighty larger than standard ammo can), that will fit just between the tire and the tub for recovery gear/tools.

Another thing that I am doing, since my struts go down into the corner, I am working on a way to keep stuff from hitting them while the lid is closed. Some stuff shifted a little and there was some interference when I was opening the trailer back at home, so wantt o avoid that.


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Have done some smaller trips. Finally did a big one. Headed out from Denver, went through St. Elmo ghost town, up over Tincup pass. Camped overnight outside Crested Butte, then headed over Pearl Pass to Aspen. Camped outside Aspen after having dinner in Aspen that night. Here is how the trailer did....

Pearl Pass with Expedition Trailer. (youtube link)

Video is a bit long, but you get to see the whole pass. Haven't done a Video of Tincup yet.. its not as "exciting" as Pearl Pass. Trailer went everywhere I did.
I did scrape the wiring just behind the Jeep, so I need to figure out a way to keep it up off the ground... Guess I need to attach it to the top of the tongue somehow.


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Love this and may copy the wood lid build! And I live in Denver too so I may bug you one day about this ha! Any issues with the wood top after all the trips?
Mmmmm 2888XL... Baby..... As you show others inside the tent.. " You will notice down in the east wing the lavish space that is available.. Now lets venture to the northern wing of the estate.." With an annex you can actually call it the north 40.