Yes, wax the plug, gel coat the plug, let dry then lay up material. After you have finished the mold let it stay on the plug several (3-4) days. Why? All resins, especially polyester will dry to the touch pretty quick but will not shrink down, harden and cure for several days....sometimes longer....depends on the grade of resin and the conditions.
I have found it much better to brush down resin then lay the glass in and satuarate it. If it has to much resin in it simply use several dry brushes to sponge out the excess with a dabbing motion. A little resin rich on the plug is ok. Resin rich in the part is not ok. Excess resin in a thin part is just extra weight and actually makes the laminate weaker because the resin can fracture "around" the laminate if stressed.
Want to know a few secrets? The older you get the less you try and keep secret...after all whats the point?
Since this is a cowl mold keep it simple. Go to the hardware store and buy fiberglass resin....yes the kind with the wax blended in it, commonly known as finishing resin. Brush a nice thick coat over the plug but don't let it make deep puddles anywhere. Let it dry..couple hours. Using the same resin wet out a single layer of the lightweight mat...not woven cloth...and keep the air bubbles out. After this layer gets dry, do another layer, let dry, then another. After you get past 2 or 3 layers, put on more than one at a time if you want.
Now, a lot of old fiberglass salts will swear up and down that you can't do this with finishing resin. Yes you can. If you do all of the laminating in one day the layers WILL adhere to each other because they are getting a chemical bond between them and no you do not have to sand between coats. You would not want to do one layer one day and then one the next because the chemical adhesion "window" of the resin closes after a day. PVA is a good thing to use on the plug since it reduces the "slip factor" and lessens the chance of the skin coat buckling up.
Build the parts the same way if you want. They will be transparent and you will have to paint them. Don't get tempted to remove a part from the mold too soon. The longer it stays in the mold the better it will retain its shape.....and....it will release from the mold easier. Hope you have as much fun with the stuff as I have!!
Mark