RE: C152 mold
The method shown in that website is basicaly it. My method is a little different. I like to use Dry Erase marker board for the parting surface. I have been using modeling clay to seal the parting board, but am planning to use bondo on my next one (The guy in Houston is using epoxy)
The finish of the part will be no better than the finish of the mold. A surface coat is a good idea, but using epoxy will produce pinholes because bubbles form during reaction. I like to apply PVA by pouring it on and letting the excess drain off. Thining it 50:50 with purified water (Dont use Acetone!) helps it coat better. If you get bubbles in the PVA, spray it with a mist of denatured alcohol to break them.