The typical release agant for fiberglass molds is a combination of coats of wax and PVA (polyvinyl alcohol) mold release. This is a water soluble (usually green) fast-drying liquid that you spray or brush on over the wax. Normal procedure is to spray on a mist coat or two and then a heavier coat. The mist coats help keep the heavy coat from running on vertical surfaces. You can also use heavy-duty hairspray from a spray can over the waxed surface. Hairspray is water-based plastic (so that it will wash out when you finally get hip and let your hair down) and a mist coat followed by a nice even coat is enough to prevent resin from bonding to the surface. Wax-wise, you would ideally want one that doesn't have a strong solvent base, like Zymol (usually available in the automotive department at places like Target) or some of the other auto waxes that say you can apply multiple coats. The solvent waxes contain enough solvent that coat number two will pretty much liquify and wash off coat number one, so you don't get much of a thickness build with multiple coats. The multi-coat waxes like Zymol (water-based) don't do this. Once coat number one is dry. you can apply number two and it will sit atop number one, rather than melt it. If you have something fancy that you want to wax, you can apply five or six coats if you want and build up some thickness. The same places that sell mold release will often also sell special mold release wax that's based on this same technology (but probably marked-up more).