I'll start by stating that I'm not brand new to fiberglass work, I've recored a few boats, replaced floors, stringers, fabricated some small stuff like mounting brackets, and small parts for RC cars from fiberglass...so I'm good with the basics. But I've always wanted to take something and make a mold from it so that I could reproduce it. I have a crappy Mercury 260 factory plastic pan that is cracked in a few places so i thought using it to make a nice fiberglass pan would be cool to try. I've been prepping it by filling some unnecessary holes, patching the cracks so that it at least will hold its shape while I am using it as a "plug". Being that it is plastic and in pretty decent shape on the exterior I figure it shouldn't be that hard to get it to release from the glass I plan to bury it in!
Looking for any constructive advice do's and don'ts that maybe I'm not thinking of...

My basic prep plan is this:

1. Patch and fill any cracks/splits and make the exterior of my existing plug as perfect as possible.
2. Wax it - looking for any advice on a mold release paste, pva, etc.

Questions:

1. Use Gelcote when laying up the mold or not necessary? I was thinking of using west system epoxy for the mold so that poly/vinylester wont want to stick to it. Although I don't plan to go into business making cowl pans - I may want to make more than one so I am aiming to make it a semi-legit mold for multiple use.
2. How many layers of mat do I need to make it? Add any good stuff like 1708? I have a ton of scrap mat, 1708, and cloth so I don't need to buy anything. Should I use some type of backing material before I pop out the plug? I thought about using some canned foam to make a backing that can be shaped flat on the bottom so that the mold can be stronger and have a nice base to sit on.

Thanks all!