: Check out the book making a kevlar canoe. It documents how to make a foam
: plug. might be of some help.

: my $.02

Another technique more suited to automotive styling is automotive styling clay. Build a styrofoam base like what has been mentioned, maybe with some plywood frames for extra structure. Then apply clay to the outside. Automotive clay is a plasteline that is quite hard, you have to heat it to apply it and make the rough form. Chavant is the supplier, New Jersy, I think. You can then add and subtract, sculpt, and finally scrape smooth with steels and polish when it is cold. You can then make fiberglass molds, or even plaster if the pieces aren't too big.