Sounds like a neat idea! How are you planning on finishing the exterior sides? That may drive what you do up top.
I actually really like the idea of plywood and foam construction and started down that design path, but realized I don't need the insulation factor and I could build out of metal quicker, easier and cheaper. I may look at building out of plywood and foam at a latter date though assuming I don't get burnt out on this project.
I agree curved surfaces are a pain to model. Luckily I don't do much of that at work. On my camper model I have I wound up just modeling everything flat full well knowing I'll put a compound bow in it when its built. What program are you using?
I'd probably finish by coating with epoxy and then paint with a white enamel, although just an epoxy coat would probably look good with a quality plywood and veneer. I think in a kit, it'd be nice if any fiberglass work were totally optional, but I think laying a layer of fiberglass over the top and any corners would be great for weather resistance.
I did a build years ago with fiberglass over foam and it was very light and strong, but it's so labor intensive going that route. I can sure see the benefit of the metal route.
What kind of design stuff are you doing at work? Any tools you can recommend?
I've been using OnShape for all of my CAD work so far, but I might need to ramp up on fusion 360. OnShape is really nice for making 3D models of stuff (I use it for 3D printing), but I haven't figured out how to take each surface of a model and spit out separate parts, and especially how to generate tongue and groove along the edges to make everything fit together easily (and strong). Might also be an option to generate stl files directly from some python code, but there's some learning curve there too.