Tim,

The next best thing to foam board is 3/16" medium balsa sheet. I prefer the foam board because it cuts so cleanly and has no grain. For the fuselage crutch, I would suggest building it up with 3/16" square balsa sticks (one long stick on each side, with a few cross-braces in between). Strength isn't that important; the crutch is really just an alignment jig for the other parts.

Please post photos of the construction if you can -- I didn't take any while I was building my prototype, and now I have a mold so the next one will be all glass.

Good luck, feel free to ask if you have any other questions or need clarification. I can't wait to see it!

Duane