As always, thanks for the responses everyone. My first pinhole camera was a shoebox. The only thing I didn't like about it was that I couldn't mount it onto a tripod, it didn't have any weight to it, and it could easily rip, fold, or tear if I dropped it. My plywood 4x5 is nice because it's has weight to it and it feels very stable, not too worried about if I drop it. Like I said though, an 8x10 camera with plywood would be quite heavy. I'll definitely give foamcore a try. Or try to brainstorm on other materials that are study and lightweight at the same time.