......West Systems Epoxy.....has much better adhesive qualitys than polyster resins..........the only drawback to using West, is that you cannot put polyester resin over it (as in future repairs) in other words epoxy sticks to polyester but polyester will not bond to epoxy......urathane/enamel basecoat clearcoat is compatable with West...........as far as fillers, I do not recall what 403 and 404 are........for strength in the groove use collodial silica #4??,use microspheres #4?? where you will be sanding and for minor pin holes only you can get away with a single component acrylic putty...........you are then ready to prime.............excellent product but more costly than polyester.........