Check out this video tutorial on how to make a fiberglass mold layup for car speakers. For fresh molds you must put several layers of wax on and I would consider PVA as well if the mold is less then a week old. Always use PVA (or equivalent) on your plug surface before molding.
The gun used in this video is just a very cheap method of spraying gelcoat on some of my smaller molds. For the larger parts, tooling gelcoat, use a HLVP gun with a 3.5mm tip. Most of the time for these small parts just brush gelcoats, you can get just as good results. When brushing leave longer then usual before resin/CSM, usually leave it overnight. This is so that any high spots from the bristle streaks have time to fully cure. If you layup over any wet gelcoat you will get alligator (crocodile) reactions on the surface. There is no maximuim time between gelcoat and resin/CSM. Gelcoats do not contain wax which means they will stay tacky and ready for resin for weeks and even months. As long as there isn't big temp changes (which causes peeling) or dust/debris in the area.
WAX = Carnauba wax (release agent).
FG = Fiberglass
CSM = Chopped Strand Matte(reinforcement)
PVA = Polyvinyl alcohol (release agent)
Plug = The original item that your creating a mold of.
Mold = A negative replica of the plug, specifically a 'tool' mold.