Trimarans have a funny shape if they are to be folded in the main hull (aka), sort of a T shape, much wider at the top. The only part that really needs rounded is the bottom and that's pretty easy. The topsides really are best made with flat surfaces, you can't see them normally when the boat's in use, they are hidden behind the amas (floats) and the tramps. If the main hull is all round shapes it's hard to get enough beam to make folding a real possibility and still be able to legally trailer it.

If it's a big tri then it's not much of an issue, since you won't be trailering it anyway.

Btw, while it could be stitch and glue, it's not really intended for that construction, it's flat panels of foam core glassed on both sides. His web site shows boats being built.

Bill H.