Is Using Scored Foam a Problem?

[AlRea]

Hi, I'm brand new to this forum and just started my build today. I'm generally following George Coe's "Bug Out" build, but plan to put this in my pickup bed, so the door has to go in the back. (I know, that big box is going to look funky in the back of my pickup, but oh well.)

My main question is about the foam: I could only find 2" foam sheets that are "scored" to make them break easily at 16, 24, and 32 inches widths. The scores are about 1/2" deep through both faces of the sheets. I read a lot of messages on the forum, but couldn't find this question addressed directly. My guess is that the foam isn't providing any real strength to the walls, it's the canvas and TB2 that provide the strength. So should I do anything like put glue in the scores, or just let them be? If I should glue them, what's the best glue to use?

Also, because I don't want to bolt through my pickup bed, I'm planning to build a 2x2 frame inside the foam box, supporting 2x2 rafters that will go through the foam at the top of the walls, and which will anchor a 2x4 rail on the outside, flush with the roof. I'll canvas over those rails, and mount D rings for ratchet straps to my anchor points in the pickup bed rails. I'm thinking this should provide enough structure to secure it to the pickup. The outside wood rails will also provide a good anchor for awnings. Sound reasonable?

Thanks for any feedback anyone can give.

[GPW]

Hi Al, Welcome !!! First off , the foam does provide structure to hold the canvas on , but it’s the combined canvas/foam that makes it so strong.
Scored foam , ( the question )… You could just ignore the scores , or fill them in with Gorilla glue , or even cut small 1/2” strips of wood to inlay into the scores , adding more strength …
Do you have a drawing or scale model ? That always helps to visualize the end result .

[Pmullen503]

You really won't need any support to handle the spans we are talking about in a truck box sized camper. I assume this will be removeable so the thing to worry about is racking when taking it on or off.

Think of a cardboard box; with the top and bottom taped up it's very rigid. But open one end and the box can flex. A long way of saying don't make you back door too big. Leave enough around the corners to act as gussets.

[AlRea]

Thanks GPM and Pmullen.

I'm attaching my plan. Won't win any prizes for the drafting, but hopefully enough to give you the idea of what I'm building. Mostly, it's a basic 4x8x4' box, but with 2x2" frame added inside (on 2' centers) and two 2x4" rails on the outside top. My studs will be secured bottom and top with Simpson Strong-Tie angles, and the 2x4s secured to the rafters using Strong-Tie brackets. I'm insulating the floor with foam, with a 1/4" plywood floor over the top of the foam.

I already purchased my door, which is aluminum framed and 29" wide and 43.4" high, so the end wall won't have a lot of foam, just 7.5" each side, and 4.5" over the top. I've modified my plan to include more 2x2 studs framing the door and where I plan to install net "shelving" in the corners by the door. Hopefully this will stiffen up that end of the box enough. I suppose I could make the end wall with 1/4-in or even 1/2-in plywood outside the foam, but that seems a bit overdone to me. I'm trying to keep this light enough that my wife and I can put it on and take it off the pickup.

Oh, and I've also purchased two 24x15" sliding RV windows, and when I decide where to place those, it might alter the position of the first stud back from the end farthest from the door.

Thoughts?

[Pmullen503]

A few thoughts; as long as the door is closed and latched, that should keep the racking under control. That and being careful when mounting and dismounting. I'd run another rail or two on the underside so your floor doesn't have to span the full width. Then you could use 1/4" ply on both sides to save some weight. Strips of UHMW polypropylene on the undersides of the runners will help them slide in and out easier.

The stud framing isn't necessary unless you need to hang something heavy from it. Otherwise, you are just adding weight.

Don't forget handles or eye bolts, something to grab and lift the box and the necessary framing to support them

[KCStudly]

Scored foam is not an issue. I used 1-1/2 thk for my walls and doors. I faired the uneven joint lines with light weight vinyl ceiling spackle before covering, both for appearances and to avoid voids. If you change your mind and switch to epoxy/FG skins, seal the vinyl with guide coats of compatible primer first (otherwise the vinyl will act like a release agent). TB2 is compatible with the vinyl.

[AlRea]

Thanks, everyone, for your suggestions. I've been making progress. I'll start a new post with my build details.