Yay, Updates!
I Joined a couple pieces of the pink foam, lengthwise, the other day, to make a single piece that would span the top of this shell. If I were keeping the shell the length of a standard bed, a single 4'x8' piece would probably work fine as a top.
I trimmed the top pretty close to the profile of the sides, and then took it all apart and glued the sides to front-most and rear-most x-sections of the shell:
It's a little hard to see, but I laid down a ton of glue along the top of each side piece as well as teh front and rear x-sections of the shell and then put ten thousand small screws in to hold the top down while it dried:
It was really hard to get a close matting between teh top and the sides:
If I were to do this again, I would probably do the top a piece at a time, rather than making one big sheet of foam and trying to glue the whole thing to the sides at once.
Anyway, once the glue is dry (2 or more days from now, probably), I'm going to use a piece of this 6" pvc tube to sand the corner between the top and the sides. I'll cut about 8" length and about 60 degrees around, and use it as a curved block to sand the contours from top to side.
I'm a little worried that, after I fiberglass this thing, that, since the top and sides are under some tension (flexing them around the x-sections), that they'll spring and warp the entire piece. I guess that, if this happens, I'll have to weld up a base plate or something to help it keep it's form. We'll see...
I went by a local auto-body place today. They didn't have any epoxy resins, but I got a baseline price for the polyester resin... It's going run ~$85 a gallon and I'll need a bit more than that to do two layers of glass on top and one inside. It'll be a little spendy to cover this thing. I need to go by "TAP Plastics", I guess, to find the epoxy resin.