Here's some pictures of the seat I built from a mold. To recap: I made a mold from an existing seat by using 3 layers epoxy and cloth. The first layer fully covered the inside surface of the seat, and the remaining layers were just scraps of every conceivable shape. If you try this, make sure you're generous with the use of the mold release. Don't skimp and ruin your existing seat. The 3 layers of cloth was enough to allow the mold to keep its shape, but still flexible enough to allow me wiggle it out of the seat.

I built-up the new seat on the mold using a full layer of cloth, 2 layers of scraps, 1 layer of roving, 1 layer of scraps, and finally 1 more full layer of cloth. Again, don't skimp on the mold release. Even with mold release, the compound curves of the seat make it a slow process of removal. I used West System graphite powder (10% by volume) instead of toner (Jay's idea) because with the graphite, no additional UV protection is required. That may be true of the toner as well, but I wasn't sure.

I built the seat in one marathon session. In retrospect, I should have let the first few layers cure for a couple hours before continuing with the roving and successive layers. There were places on the finished seat where the 1st layer pulled away from the seat, and instead of a shiny finish there, the weave of the cloth was exposed. I think the weight of the cloth pulling over the edge of the mold lifted the cloth up. A few hours wait after the first few layers would have been enough to prevent that. I can test that theory on the next seat.

This was a very satisfying sub-project. You don't have to be as fastidious with mixing the epoxy (as far as worrying about air bubbles), you don't have to worry about applying too much epoxy, you don't have to squeegee, you can use all kinds of ridiculous pieces of scrap cloth, and still the thing turns out pretty good.

Here's a few pictures of my progress. Notice in the final photo there are some rough areas around the perimiter. That's where the cloth pulled back a little. I'm not going to bother trying to fix them; they're not in places that you can actually feel them while sitting on it. All-in-all, I'm very pleased. Now I will have a happy bottom.