I'm relatively fresh to working with epoxy, but have been using it on the little 1/24th scale Delphin sub I'm working on. The process is similar to polyester work, with a few small differences. One big advantage is that epoxy is almost odourless, and any slight smell it gives off is far from objectionable I find.
You can get epoxy gelcoat, but you work with it a little differently to polyester based gelcoat.
Whereas polyester gelcoat tends to be an air inhibited resin, epoxy resin is basically a thickened lay-up resin, with colloidal silica blended in to bulk it up and avoid it sagging. Many people mix their own epoxy gelcoat, but I find it can be tricky getting the silica to thicken the resin in a consistent way that gives you a nice smooth resin like the pre-blended versions.
When you brush the gelcoat on you leave it for about two to three hours, then apply subsequent layers of epoxy. If you leave it to cure, the subsequent layers won't chemically bind with gelcoat, so you need to rough it up to get a good mechanical bond.
The only reason to use a gelcoat with epoxy would be to resolve detail in the mould, especially if using hand layup. Other than that it's better to go straight in with the glass, and build up with successive layers of cloth, which gives an incredibly strong but lightweight composite.
Epoxy is a much better adhesive than polyester, so you can lay lots of cloth layers without fear of de-lamination, with polyester it's generally advised to put a layer of matt in between two layers of cloth. I tend to use only matt for polyester anyway, as the extra weight isn't much of an issue for the things I work on (Delphin was the exception to the rule), and it's more than strong enough.
