If you want a material that is easy to fair, easy to work with, cost effective, and isn't attacked by resin, try wood. If you want to build multiple boats you could make a wood plug and layup a series of boats, but if you're just building one why not leave the wood in the boat. If you're after a lot of strength you can go with thinner wood strips and more layers of glass/epoxy. The wood is just a spacer between the inner and outer layers of glass, which provide much of the strength in this type of construction. By the way, George Roberts is the guy to talk to about this type of construction.