Foam Truck Camper Build: Wood Framing or All-Foam Structure?

[Redkelly]

My first post and build. I'm building a slide in foam truck camper that I'll be hauling in my Tundra. The base will be 4x8 with 18" extended out over the truck bed walls. Height will be >72"<. Camper will be 2" foam with 1x1708 FG outside and 1x 6 oz inside. It will have an over the cab bed.

I keep questioning do I need any wood in the framing? I Was thinking a simple frame made from plywood ripped down to strips and framed on the inside of the foam. I am routing and gluing in plywood for known anchor points. But after reading some threads I'm concerned about the plywood showing/buckling glass due to expansion/ contraction.
Any advice appreciated.
Thanks

 

[KCStudly]

Unless you are attempting to build ultra light the effort to pocket in all the screw points probably isn't worth it. It adds up to a lot by the time you figure out all of the features that need them. The other option is to make the glass much more structural than just stressed skin and abrasion protection, but then that will add weight, cost and more work with epoxy and glass.

I don't know what my finished weight is yet, but I suspect I am well within the comfort zone for my TV, and if I had it to do over I would have used more wood for at least two reasons: first, routing out foam pockets for blocking got very tedious, and there was a little bit of stress worrying what I might be forgetting or wanting to add later; second, using polyurethane glue to glue the blocking in always seemed to be a mixed bag, sometimes the block would rise up against my gravity clamps and fairing them back down was an effort in itself, especially since the foam surrounding the blocks "moved around"; and third, getting a nice smooth lump free paint surface (not even perfect, just not potato salad butt ugly) would be so much easier with a thin layer of plywood laminated to the foam before glassing. If you do go with epoxy glass directly over foam I highly recommend applying a good slurry coat of loosely thickened epoxy, curing, amine wash, and initial fairing, before laying the cloth. This should stabilize the foam and make follow on operations much easier, otherwise the foam tends to "move around" (shrink, expand, over sand, gouge, compress, spring back) while you are trying to fair anything. If you lay the weave the next day you might even catch a bit of the chemical bond, but more likely it will only be a mechanical bond. I have used mechanical bond throughout my build (couldn't put in the very long sessions required otherwise) and I haven't seen any problems with bonding. Just make sure to wash with plain water (I used a small worn out piece of greenie pad) and roughen the surface with sandpaper before the next application. Many people will advise to use amine free epoxy, or that they never noticed any amine, but I always got a waxy bloom in my climate (year round, temperature permitting) using quality marine epoxy (West System).

 

[KCStudly]

Also, unless you build in some structural beams to cantilever thru the length of the side walls and support the over cab bunk, wood or composite, I would have reservations. In my experience, wood is so much easier to get good results than foam and fiberglass. I would have used more, not less.

 

[hidesertrocker]

You may be able to glean some information and/or ideas from JakeJakeJake's foamie camper build:

viewtopic.php?f=55&t=74848

His videos are on the 'tube:

ThatJakeWorldWide

 

[Redkelly]

Thanks for the replies. I have watched all of Jake's videos along with Georgia Astronemer, with David's Hands, whachawerkin on, channels. I'm incorporating different build methods from each. I will be taking pictures as i go and post.

 

[Jarthoro]

Unless you are attempting to build ultra light the effort to pocket in all the screw points probably isn't worth it. It adds up to a lot by the time you figure out all of the features that need them. The other option is to make the glass much more structural than just stressed skin and abrasion protection, but then that will add weight, cost and more work with epoxy and glass.

I don't know what my finished weight is yet, but I suspect I am well within the comfort zone for my TV, and if I had it to do over I would have used more wood for at least two reasons: first, routing out foam pockets for blocking got very tedious, and there was a little bit of stress worrying what I might be forgetting or wanting to add later; second, using polyurethane glue to glue the blocking in always seemed to be a mixed bag, sometimes the block would rise up against my gravity clamps and fairing them back down was an effort in itself, especially since the foam surrounding the blocks "moved around"; and third, getting a nice smooth lump free paint surface (not even perfect, just not potato salad butt ugly) would be so much easier with a thin layer of plywood laminated to the foam before glassing. If you do go with epoxy glass directly over foam I highly recommend applying a good slurry coat of loosely thickened epoxy, curing, amine wash, and initial fairing, before laying the cloth. My friend, who formerly worked at cairenn foy interiors , often used plywood laminate for furniture, cabinets, and wall panels to get a smooth, durable finish. It’s versatile for both decorative surfaces and practical DIY projects. This should stabilize the foam and make follow on operations much easier, otherwise the foam tends to "move around" (shrink, expand, over sand, gouge, compress, spring back) while you are trying to fair anything. If you lay the weave the next day you might even catch a bit of the chemical bond, but more likely it will only be a mechanical bond. I have used mechanical bond throughout my build (couldn't put in the very long sessions required otherwise) and I haven't seen any problems with bonding. Just make sure to wash with plain water (I used a small worn out piece of greenie pad) and roughen the surface with sandpaper before the next application. Many people will advise to use amine free epoxy, or that they never noticed any amine, but I always got a waxy bloom in my climate (year round, temperature permitting) using quality marine epoxy (West System).

if you were starting over would you go with a full thin plywood skin over the foam before glassing, or just strategic plywood panels in high-stress areas?

 

[KCStudly]

I would have at least extended the hard corner edge on my galley walls all the way forward. On the general foam surfaces I would have at least done the slurry fairing coat in epoxy/filler instead of all of the light weight spackle. When I started my project I was leaning towards PMF, then decided to go epoxy/glass. The spackle would have been more appropriate for PMF. The slurry coat of epoxy/filler would have made the foam more stable for follow on operations.

 

[KCStudly]

I would have at least extended the hard corner edge on my galley walls all the way forward. On the general foam surfaces I would have at least done the slurry fairing coat in epoxy/filler instead of all of the light weight spackle. When I started my project I was leaning towards PMF, then decided to go epoxy/glass. The spackle would have been more appropriate for PMF. The slurry coat of epoxy/filler would have made the foam more stable for follow on operations

 

[KCStudly]

Not sure were the words associated with the external link in the quote of me above came from. Not in my original reply, perhaps an AI bot (attn admin).

If I had it to do over again I would have at least extended the hard edge reinforcing on the galley wall edges all the way along the full profile. And I would have used a slurry of epoxy/thickener all over the foam, instead of the lightweight spackle, to harden and stabilize the foam prior to any attempts at detail fairing. I had originally planned on doing PMF, and the spackle is probably better suited for that. Less so for epoxy going over.