Getting the wheel pants ready for paint is not too bad. The gel coat makes it pretty easy. First, fill all gashes, pits and holes with your filler. I have been using epoxy/glass filler. A 2 part epoxy mixed in with glass powder from Aircraft spruce. Sanding with this stuff is a breeze.
For primer on all fiberglass parts I used select primer - surfacer 421-20 with the activator 483-83. A dupont Primer from their Nason line. Recommended by them for the primer layer for Imron top coats. Fills and sands easily. Also dries fast. Everything is surface prep'd with Acetone. Expect several sessions of priming and sanding to get the perfect finish