Basic forms are now cut out:
They're heavier than I thought they'd be; this isn't Styrofoam® after all. So I'm planning to cut out most of the insides.
The plan now is to fasten the boards together with drywall screws, shape the outside, then take all apart, cut out the insides and glue together. I want to shape the outside first, especially at the bow, because then I'll know how far I can go with the hollowing-out process. I'll be cutting out sections of each board and leaving enough material on the outside for strength. Planning to not treat the inside at all, to save weight.