make a foam replica of your design, fiberglass it (at least 7 layers), then bondo glass it..sand, test fit. The "lost foam" method of mold creation is very time consuming. Most pros now use other ways of laying up a mold including balsa wood, egg cartons, expanding foams, etc. etc. Anyways, back on topic. As far as creating a perfect mold from a design goes, I have personally spent up to three months on just the mold work. There's people who can do it faster, but they're usually companies like APC who have design teams and use the old way of clay building. Just my 2 cents, hope it helped and good luck.