I've molded cowls for all my stunters and some others. I carve the plugs from balsa and finish them with something other than dope: dope sticks to Frekote 700, the release agent I use. Then I build up a base for the cowl out of modeling clay (plasticine) on a board covered with MonoKote. I give the cowl plug and board a toot or two of mold release. I then put a wood frame around the plug, holding it to the base with clamps. I pour casting epoxy over the plug to form the mold. It is rigid when it hardens, so you can get the plug out only if it has some draft. If not, use two-part silicone resin. Now I remove the plug and toot Frekote 700 mold release on the mold. You can also use PVA as mold release. The finish isn't as nice, but it works, and you aren't going to make a lot of parts, so you can afford to sand them. You can use nonwoven carbon (mat, veil, tissue) on the cowl surface to avoid the bumps you get with cloth. Use .5 oz. or 1 oz./ square yard stuff, though, not the really light material that's fashionable for doping on stunt planes. You'd sand right through the light stuff. You'll have to cut darts in the nonwoven stuff to get it to lie down in the mold. The guys above are correct about using woven cloth: the nonwoven stuff has no strength. I make the body of the cowl out of a couple layers of 2-oz. (or so) carbon cloth. I use runny epoxy, usually Epon 815 with DTA hardener. There are a couple of ways of getting the right fiber/resin ratio. The easy way is to cram the carbon in the mold, put on extra resin, then put in a layer of Teflon with little holes in it for the excess resin to escape through, then a layer of polyester batting or paper towel to sop up the excess epoxy, then the vacuum bag. The best bag material is Stretchlon. CSTSales.com can fix you up with the stuff to do vacuum bagging if you don't have it. If you made your mold from silicone, the pressure will press the cloth weave into the silicone, making the cowls difficult to finish, as the people who finished the B-17 cowls I made can attest. If you want to make an axisymmetric cowl like that, I can tell you a much better way to do it, based on painful experience.
I left out details and pictures because nobody will read this anyhow. I'll put in some effort if somebody's interested.