DIY Over-Cab Camper build help...Not an in-progress build (YET)

[teelong83]

Thank you all for the input and suggestions.

Foam only?! Foam is a core material... good insulation and good for structural panels. I don't think bedliner over foam is going to help much. Fiberglass over the foam is definitely viable, though.

I'm building a camper now with PVC foam core and wet-laid fiberglass and carbon skins. I built a couple in the past with cheap XPS and wood slats in the core, and 2.7mm Luan ply skins; the later one encapsulated with a layer of fiberglass. I kinda favor that method. It's simpler DIY, not as messy, quite light, the embedded wood gives you lots of hard points, and it's cheap.

I put this together awhile back to estimate panel weights and cost. Ask questions!

HOLY COW @rruff That is a spreadsheet that everyone can/should appreciate. It should be pinned to all DIY threads! I love breakdowns and getting lost in the details like that. Very helpful and much appreciated. Do you recall if the weight of the finished panels were per sqft of both sides or just one finished side? i.e. 4x8=32sqft but is that one face or both sides so the weight would then have to be doubled?

I may have misspoke....no, mistyped(?) or whatever. I don't intend to use 100% foam and nothing else...I know there are severe limitations in that regard. However, I do want to keep it light and I realize there will be some amount of wood and/or aluminum. I am not against the PMF method, but I don't know if it would "replace" a fiberglass epoxy job. I do plan on having either luan / pretty ply or a product called "signabond" (which is thin aluminum skins on a composite core for a 3mm thick panel) on the inside of the camper for aesthetics, but it will also add strength. I am leaning heavy to the signabond side. It is available in colors and is about $60 for a 4x8 sheet locally.
In doing more research the past few days, I have convinced myself that the truck bed liner won't really add any strength properties, but I plan on using it on the outside in lieu of paint/gelcoat...with weight being considered.

 

[rruff]

The 2 right columns are totals for the panel. Paint is not included, nor materials used to join panels together. For the PVC foam+ FG panels I'm building there was quite a bit of filler (fumed silica and epoxy) and extra fiberlgass in the edges and corners... more mess!

If you use XPS foam, I highly recommend texturing with a wallpaper roller and really working the glue or epoxy into the perforations. Then do your skin applications before it cures. Nothing sticks to cheap XPS very well, plus it's quite weak.

In my experiments PMF was very weak compared to epoxy-FG layup. And it creeps. It's more like a heavy duty coating than a structural skin IMO.

I really liked having the wood interior of the luan. When I built that camper, luan was better quality than it is now, though. If you can get marine ply locally you might look at 3mm okoume. It will cost a lot more but it will be light and high quality.

The signboard you mentioned is near 1 lb/sq ft in the lightest configuration... much too heavy IMO.

I painted my exterior with Corotech V515, 2 part polyurethane. Would not call it a success! It should be very tough, but it took a long time to cure (probably put on too thick), and the color was quite uneven (an issue with grey paints?). Bedliner is thick and heavy... might be overkill if you already have a strong/hard exterior layer.

 

[Peter_n_Margaret]

Closed cell polyurethane foam has almost double the insulation of expanded polystyrene foam of the same thickness and better structural qualities.
The 1.5mm of glass plus gel coat is laid up wet-on-wet and vacuum bagged.


We are sitting on the pop top. It has no underside support structure. We have had 4 people on chairs up there without issue.

Cheers,
Peter
OKA196 motorhome

 

[IdaSHO]

Closed cell polyurethane foam has almost double the insulation of expanded polystyrene foam of the same thickness and better structural qualities.

There is zero reason ANYONE should consider Expanded Polystyrene (EPS)

Instead, Ill always advise Extruded Polystyrene (XPS)

And specifically what foam panel are you referring to when you say Polyurethane?
Polyiso? Or a true polyurethane?

Polyiso isnt terribly great for road travel as it breaks down with vibration.
Polyurethane sheet is typically pretty heavy.

 

[Peter_n_Margaret]

My new build uses Polyurethane 20mm plus 1.5mm of glass per side weighs 6kg/m2 and is fully structural. No other framing required.
Roof will be 30mm plus glass for better insulation.
My existing vehicle (16mm plus glass) has 250,000km of bush travel with zero deterioration.
Cheers,
Peter
OKA196 motorhome

 

[rruff]

If I had it to do all over, I'd look real hard at the way P&M's camper above is built. It's the same way Styromax in Aus does theirs, only they use XPS core. If you are building a simple box (all 90 deg edges) it's an easy way to go. Frankly... it seems janky as hell to just glue the edges together like that, but apparently it works! ? One addition I'd make is aluminum or extruded FG angle on the outside edges, and I think I'd use thin ply for the interior skins (instead of the FG), with wood pieces in the edges.

If you want to make it more aero, carve a stack of XPS foam into a rounded shape that fits the front of the cabover. Fiberglass and paint it, and glue it on there.

Here are some specs from a FG skin manufacturer who sells out of Greenville, SC. 1.4mm with gelcoat is as light as .39 lb/sqft. Don't know what the price is. https://www.vetroresina.com/media/uploads/allegati/4/us-20042020-matstuoia.pdf

 

[Peter_n_Margaret]

This is a Defender chassis built by a friend 15 years ago and still great (it is pale green now, not white).
The camper is DIY sandwich panel using closed cell polyurethane core and glass both sides made wet-on-wet with a vacuum bag on a shed floor.
The rounded corners were filled on the inside with foam, hand shaped and then glassed by hand.
Furnitre is all sandwich panel. There is no frame of any kind. The body is bolted to the chassis via multiple rubber blocks and glued to the cab.

We recently did a trip together. Here is a snippet of the roads via a dash camera.

Cheers,
Peter
OKA196 motorhome

 

[IdaSHO]

My new build uses Polyurethane 20mm plus 1.5mm of glass per side weighs 6kg/m2 and is fully structural. No other framing required.

6kg/m2 works out to roughly 1.5lb/sq ft Not bad. But heavy enough it better not need framing
What R-value are you getting at just 20mm?

For comparison sake...

My (over-built) wood framed, 1-1/2 XPS (R7.5), with 1/8"ply interior and 6mm marine ply exterior w/ glass, epoxy, and coating still weighs less than 2lb/sq ft.
I think the final tally was a hair less than 1.8lb/sq ft. The shell weighed right about 700#, which is about right as it is very close to 400sq ft of surface.

Considering the thick skin and epoxy, Id also venture a guess that it is considerably more robust. This thing is bomb proof.
Bouncing it off of branches/trees as we have, personally, Id be leery of a unit made with just foam and glass.

 

[mobile007]

Closed cell polyurethane foam has almost double the insulation of expanded polystyrene foam of the same thickness and better structural qualities.
The 1.5mm of glass plus gel coat is laid up wet-on-wet and vacuum bagged.
View attachment 718009

We are sitting on the pop top. It has no underside support structure. We have had 4 people on chairs up there without issue.
View attachment 718010
Cheers,
Peter
OKA196 motorhome

Very Impressive

 

[ITTOG]

6kg/m2 works out to roughly 1.5lb/sq ft Not bad. But heavy enough it better not need framing
What R-value are you getting at just 20mm?

For comparison sake...

My (over-built) wood framed, 1-1/2 XPS (R7.5), with 1/8"ply interior and 6mm marine ply exterior w/ glass, epoxy, and coating still weighs less than 2lb/sq ft.
I think the final tally was a hair less than 1.8lb/sq ft. The shell weighed right about 700#, which is about right as it is very close to 400sq ft of surface.

Considering the thick skin and epoxy, Id also venture a guess that it is considerably more robust. This thing is bomb proof.
Bouncing it off of branches/trees as we have, personally, Id be leery of a unit made with just foam and glass.

Did you use metal in your frame in the back and possibly up front? Just saw the redish/brown paint so I was curious.

 

[rruff]

Yes, he has a some steel in the bottom... from under the cabover to the rear.

Kenny... where is that awesome build thread you had?

 

[IdaSHO]

Yep, anything RED is a thin wall square tube steel frame, with the intended purpose of a legit structure to fasten jacks to.
The entire core of the tubing was filled with a closed cell spray/expanding foam, in hopes of eliminating condensation and rust.

Build thread (2011 to 2012-ish) was over on Pirate.
Since lost to the sands of time.

 

[mobile007]

My new build uses Polyurethane 20mm plus 1.5mm of glass per side weighs 6kg/m2 and is fully structural. No other framing required.
Roof will be 30mm plus glass for better insulation.
My existing vehicle (16mm plus glass) has 250,000km of bush travel with zero deterioration.
Cheers,
Peter
OKA196 motorhome

Do you have any build thread that shows these interesting processes that you describe?

 

[mobile007]

Thank you all for the input and suggestions.



HOLY COW @rruff That is a spreadsheet that everyone can/should appreciate. It should be pinned to all DIY threads! I love breakdowns and getting lost in the details like that. Very helpful and much appreciated. Do you recall if the weight of the finished panels were per sqft of both sides or just one finished side? i.e. 4x8=32sqft but is that one face or both sides so the weight would then have to be doubled?

I may have misspoke....no, mistyped(?) or whatever. I don't intend to use 100% foam and nothing else...I know there are severe limitations in that regard. However, I do want to keep it light and I realize there will be some amount of wood and/or aluminum. I am not against the PMF method, but I don't know if it would "replace" a fiberglass epoxy job. I do plan on having either luan / pretty ply or a product called "signabond" (which is thin aluminum skins on a composite core for a 3mm thick panel) on the inside of the camper for aesthetics, but it will also add strength. I am leaning heavy to the signabond side. It is available in colors and is about $60 for a 4x8 sheet locally.
In doing more research the past few days, I have convinced myself that the truck bed liner won't really add any strength properties, but I plan on using it on the outside in lieu of paint/gelcoat...with weight being considered.

Where will you be sourcing your signabond from?

 

[teelong83]

@mobile007 I called around to a few sign places in town and found 2 that deal in the signabond. Both had the same pricing, and probably sourced from the same distributor. They both said that they would not recommend it being used for a structural board on the outside, but used on the inside for a finished look would be perfectly fine.