Thanks for the posts, guys!
I picked up a test batch of resin, hardner, twill weave glass, and some matting that, per a short demonstration by the nice fellow at TAP Plastics, added 10x rigidity to the piece:
Seems that I will need ~3 gallons of resin for this, given it's size. What's the best way to do the seams where sheets of cloth meet? The cloth is about 3' wide, so I'll have several seams along the shell. Should I sand the foam a little lower where the sheets meet so there isn't a rise that I have to body-fill around? That makes sense to me...