Bondo products will work, but they are polyester based and have the highest VOC of all the resins we have been discussing. So a respirator is a MUST, and if you do it indoors the stink will linger for a long time. And by stink, I mean harmful vapors. Generally on pep you resin the outside, the inside, lay fiberglass on the inside for support, and bondo on the outside for detail. You can glass the outside and then bondo but you will lose quite a bit of detail from the pep piece. I prefer cloth over mat because its less messy, but either would work. As for sandpaper, bondo sells an autobody pack with grits from 250-600. Add some 80-100 girt for taking down high spots and that should be enough unless you are going for a glossy mirror finish. Or go with a set of sanding sponges. Course, medium and fine.