What product can I use to cover the fiberglass strands that show on the surface of the underside of a model a ford fiberglass fender. I would like them to look smooth on the underside.
You can treat it similarly to an exterior body repair by using epoxy, poly putty, more epoxy and/or high build primer, then whatever topcoat you want to use. The kind of topcoat to be used will dictate the finesse level required on the finish work.