Mounting a composite camper box on 4x4 E350 chassis

b. rock

Active member
An E-350 needs about 6" to fit a solid axle under the engine with any reasonable amount of up travel. Stock floor has recesses for wheel wells. Look up pictures of a bare cab/chassis and you'll see what I mean about the bump.

Edit: this is why the Transit frame is so appealing - it's flat. The tradeoff is just a lack of solid axle compatibility/off road ability and initial purchase price (if going used). No idea what the Chevy express frame looks like.
 
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ScottPC

Active member
Some may find this info interesting and informative from Unicat. While Unicat is dealing with heavier loads and larger vehicles, many of the objectives and principles apply:


starts at 1:15 Note: The subframe is integrated into the bottom of the box.

Body to Chassis mounting:
 
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Victorian

Approved Vendor : Total Composites
Some may finds this info interesting and informative from Unicat. While Unicat is dealing with heavier loads and larger vehicles, many of the objectives and principles apply:


starts at 1:15 Note: The subframe is integrated into the bottom of the box.

Body to Chassis mounting:

After working for Unicat, I can assure you that these subframes and knowledge are the real deal.
 

ScottPC

Active member
After working for Unicat, I can assure you that these subframes and knowledge are the real deal.
I'm sure there are other systems that work well, but to have it explained, demonstrated, and backed by 30+ years of experience it hard not to consider it the best solution. The next question becomes if my application is smaller in scale (lighter box / lighter vehicle) is there another method that performs as well and potentially a little more affordable? That said, if this sort of solution is more expensive but still a relatively small percentage of the overall build, it's worth it given how critical it is to the overall success of the project and peace of mind it brings.
 

Victorian

Approved Vendor : Total Composites
I'm sure there are other systems that work well, but to have it explained, demonstrated, and backed by 30+ years of experience it hard not to consider it the best solution. The next question becomes if my application is smaller in scale (lighter box / lighter vehicle) is there another method that performs as well and potentially a little more affordable? That said, if this sort of solution is more expensive but still a relatively small percentage of the overall build, it's worth it given how critical it is to the overall success of the project and peace of mind it brings.

With yours:
Fixed mounted at the front, springs for movement in the middle and rear. Done.
 

cabnetguy

Member
Hi Victorian, I will be using the u-haul box that came on my truck (cut away E-350) for my build and will mount it like you suggested, with the box fastened directly to the cab. Instead of fixed plate at the front of the box, what due you think about using the rubber mounts that Ford recommends to mount boxes? My thought would be to match the flex in the rubber cab mounts to keep from having stress at the cab/box joint and then use spring mounts middle and back on the chassis.
 

nillum

New member
Hi, I'm a newbie here and I am really interested in building my own camper using a tc system. I am wondering if anyone has sorted out the sub frame captured spring vs pivoting frame? Also cab attachment, box fixed like a box truck or independent and a using a accordion gasket
 

fjefman

Member
I feel the need to resurrect this thread from the grave just to clarify something.

Like a few others here I'm considering building a camper on an E-Series chassis. My plan is to mate the box solid to the cab and use the factory fleet frame spacers with OEM body mounts to get the last surface over the frame mount. I am looking at a SIP fabricated box which will essentially be rigid mounted to the frame with little flex except through the factory body mounts. This is essentially how most vans are made (solid rigid body bolted to the frame with body mounts and there is no flex in the factory body. This would get the floor of the box essentially at the same height as the floor of the cab (depending on how thick/insulated the floor is.

(almost) All RVs built on the cutaway chassis are essentially made the same way with a rigid mount to the cab. They usually have a very crude system (subframe) to get the box flat over the frame hump so it isn't like they have any designed in flex...but this crude system usually adds 6-8" of height to the floor which is not at all ideal.

A build this way would go against most of logic on this thread, and apologies if I'm wrong, but it doesn't seem like anyone here actually has experience building something like this on the e-series chassis so say right or wrong. So...has anyone actually tried a ground up build yet on a cutaway chassis?
 
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rruff

Explorer
This is essentially how most vans are made (solid rigid body bolted to the frame with body mounts and there is no flex in the factory body... (almost) All RVs built on the cutaway chassis are essentially made the same way with a rigid mount to the cab. They usually have a very crude system (subframe) to get the box flat over the frame hump so it isn't like they have any designed in flex...but this crude system usually adds 6-8" of height to the floor which is not at all ideal.
RVs don't have a rigid box for starters... but it sounds like yours will be rigid. Plus RVs aren't designed to go offroad.

You'd probably be fine rigidly attaching to the cab, but only if you use a pivot or spring mounts aft of there. Otherwise your box will be taking all the torsional loads.
 

fjefman

Member
Thanks for the reply @rruff there is really two points in here to consider, right?

#1 - Mounting the box solidly with the cab.
#2 - Flex mount in the back.

As to #1 - To me this is an absolute. In my mind there are two huge benefits to using the e-series vs an f-series for a build. The first has been mentioned by the OP and is a shorter front end; compared to a friend's F-250 my current E-350 is 25" shorter from the front of the bumper to the front of the door seam. The second benefit is the walkthrough from the cab to the box. A van chassis is designed that way, the seats are higher and designed more like chairs with nothing between them, so it is easy to just spin around and walk to the back. This means when in camping mode the cab is actually part of the usable space (especially with pivoting seats). This provides essentially another 3' or so of living space vs a a dual-seat truck chassis. I know a tunnel bellow can be used between the cab and box but it takes up space and adds complexity to the entire setup, and I think it is unnecessary.

As to #2 - Yeah, I'm not denying that flex is better for a camper that is intended for frequent off-road and critical for large vehicles where the chassis alone can weight 10K+ lbs, but there are a few things to consider:
- Very few people actually do real offroading in their camper. I live in Georgia (USA) and my limitation for off-road use is much more likely to be overhead tree/branch clearance rather than what is in front of me on the ground. A 23-24' long, 10' tall, 7' wide vehicle can only physically fit in certain areas. That said, yes, in the desert overhead clearance is much less an issue so it is easier to get a big vehicle into some more extreme places, but that certainly isn't my use scenario.
-For an smaller vehicle like an e-series with a 12-13' box and lightweight build with a stiff box, the box itself is essentially going to add stiffness to the frame...just like a standard van body...so I really think accounting for large flex is really a non issue...and here is my logic is this:
-Base platform considerations - there is essentially zero flex is the OEM van bodies and they are mounted "rigidly" the the frame. Some people are taking their vans to extreme places and never have I ever seen a report of an issue with too much or too little flex or damage to vehicle because of its mounting type. So, a stiff box can be attached to the frame with no issues.
-Available data on the platform - there are hundreds of thousands of RVs and utility vehicles built off of the e-series chassis and almost all styles (except for some of the work boxes and larger U-Haul type vehicles) have a the box firmly attached to the cab and mounted "rigidly" to the frame. I know a few people who have put their e-series RVs in crazy places for decades and never had an issue.
-The forces are so much different for a smaller vehicle than for a larger one so it isn't a one-size-fits-all solution. Gravity effects an ant very differently than a human. Sure, the e-series is not light, but it certainly isn't as heavyweight either so the forces on the vehicle are different. There is a great comparison on relative sizes of different platforms in this thread - https://expeditionportal.com/forum/...like-sportsmobile-to-earthcruiser-4x4.214417/
-My off-road use will likely to be very limited...sure I'll take it off pavement regularly, probably ever time I'm headed out in it, but it certainly won't be extreme off-road and it will likely account for just 2-3% of the total miles driven in a given year. Even then I'll be going slow as I will have a motorcycle on a rear hitch, and I really only need to get as far as a good campsite where the camper will be parked to serves as basecamp for days to weeks. My bikes are my off-road transportation.

So, for perspective, for my build I'm specifically looking at starting with a new E-350 or E-450 cutaway chassis with 158" wheelbase and DRW (I want the capacity for a bike or two on a rear rack). My box will be 12-13' total length, just over 7" wide and with 6' 6" interior height, and as I mentioned previously will be built with SIP panels. If I'm an idiot for thinking about doing this please let me know. Otherwise I hope to start the fun build later this year.
 

Victorian

Approved Vendor : Total Composites
You can't compare a commercial truck body to a camper body.
1. commercial truck bodies are usually MUCH heavier than a lightweight camper (at least in our case)
2. commercial truck bodies are allowed to flex. They do! Hence a short lifespan . Interior outfitting will stiffen the camper. This means if not the camper, what will flex then?
3. a camper should not flex as otherwise your cabinets, windows, doors are popping apart in no time.
4. Commercial trucks have rigid subframe to avoid the need for wheel wells.
5. Do yourself a favour and eliminate the frame twist from the camper. Imagine having spend all the time, money and effort into this house on wheels just to find out 6 months down the road that your body is cracking and items start to fail.
 

vintageracer

To Infinity and Beyond!
How are Ambo boxes mounted?

Ambo boxes are well built, stay connected to the vehicle frame mounting system whatever that is and survive rollovers. These boxes have to add stiffness to the frame one would think and that may be good or bad from an off-road perspective.



 
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rruff

Explorer
If I'm an idiot for thinking about doing this please let me know. Otherwise I hope to start the fun build later this year.
I certainly can't say for sure... it just seems like a risky proposition. And I understand your desire to keep things simple. But I really don't think the original van body, or service bodies and boxes are a good example. They generally have single walls and are open at the back (ie not a closed box), so they can twist pretty easily. Refrigerator boxes and ambulances seem like they'd be quite stiff, but I don't know what if any accommodations have been made in the mounting, or if there are frame reinforcements. In the video above you can see that the ambo box is very stout and there is no evidence of torsional flex at all as it's being rolled... so I'd guess a rigid mounting, and a reinforced frame.

The thing you want to avoid is having your box be the most rigid part of the system, unless it's specifically designed to take the torsional loads on its own. The challenging situation is when all or nearly all your weight is on two diagonal wheels. That happens all the time where I go, since trails will often cross a gully at an angle.

How exactly are your sips constructed?

One thing you could do is build a torsionally stiff steel subframe that your box mounts to, and then reinforce the frame around the most forward mounting point, which I'd expect to have the most stress.... then use poly mounts between the frame and subframe. This is my fallback if my pivoting scheme is unsatisfactory.
 

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