To keep parafin from clumping as you paint it on, you can warm the mold some.

If you want to reinforce a fiberglass seat, you can mold ribs into it by shaping glass channels joined to structure with EPP foam.

Here's another approach (untried, of course): Get a very thick, soft cushion (like a sofa cushion). Lay fiberglass and epoxy directly on it with an extermely fast cure hardener. When the epoxy is close to going off (or before) sit on the fiberglass that is on the cushion (lay plastic over top). Let it set up, and you have your mold. Instead of a perfect impression of your butt, I think you'll get a seat that feels comfortable.

This sounds painfull.

> I burned off any adheared pieces of plastic with a propane tourch.