Setting up forms and running stringers, then fitting and cutting panels, then removing (or keeping) the stringers and building the boat S&G style is easily done. It saves the trouble of using software or manually lofting to establish the panel shapes. Here, I'm taking about 'forms' as removable molds, not the fuselage-style forms which control the longeron (stringer) positions and are part of the finished boat.

Thanks, John - that's pretty much exactly what I'm (now) talking about. The only reason foam entered the picture, is I was thinking you'd want to minimize the number of panels. If you went with thicker plywood then you'd presumably need to cut more panels to get it to conform. If you went with thinner plywood you'd presumably need fewer panels (since it's more flexible) but now you'd have to worry about strength. That's where the "hybrid" notion came in - thinking that if you retained the stringers, they could provide the strength, so now you could use the thinner plywood and thus cut fewer panels. However, now you'd have to deal with a core of varying thickness which seems like a pain to glass. That's where the foam comes in - you want the flexibility and strength of the thinner plywood, but the additional "bulk" to match the core thickness set by your stringers. That's really all I meant.