Custom seats

I really like the idea that Ross has. Creating a copy of a fiberglass seat. http://ross.secant.com/kayak/buildingInfo/seatmold.htm . Problem is I don't have a seat to copy. I have created a simple seat out of pink foam. I was planning on filling the seat with plaster or something similar, covering with plastic, and sitting in it until dry. Then shaping it. Cover with epoxy to make it smooth. Then using it as my mold. Sound stupid? Ideas ????

Derek