As I was planning on painting
my FGRV I filled the rock chipped areas with epoxy into which I mixed micro balloons. The micro balloons thicken the epoxy so that it acts like using spackle in a dent on drywall.Easy to sand so I do a very slight overfill for an invisible repair avoiding having to do a second application.
Rebuilding edges and corners. It really depends on where it is as to what to do with it. If it is a corner that can be made to look good just by rounding over to create a radius that is what I would do versus trying to repair it. If the edge is slightly damaged but one that typically has some type of vinyl edge trim over it I would do nothing other than smooth off any rough edges because the damage will be hidden under that trim. My last choice would be to use some lightweight fiberglass cloth. If you try to accomplish the task by putting resin onto the trailer and then pressing cloth into it then that would make for a very frustrating, drippy messy so let gravity be your friend and put the resin on the cloth while the cloth is lying on a horizontal surface.
How easy it is to rebuild with fiberglass cloth? The work is not difficult in itself. There is a "trade secret" method to use for applying the cloth that makes it pretty fast to do and not overly messy. Apply the resin to the cloth and spread it into the cloth with a sqeegee while the cloth is lying flat on a table. I cover the table surface by taping down acut open, large plastic garbage bags so that I can toss the mess away afterwards. After your strip is prepared then take it over the the RV and use a small throwaway type of paint
chip brush and/or the sqeegee to smooth it onto the surface.
Very thin fiberglass cloth is called E-glass ...that name comes from the electonics industry where they use it to build bases for circuit boards. You can purchase it from places such as Tap Plastics, surf board building shops and some boat building suppliers. You will not find it in auto parts stores, hardware stores or places such as Home Depot. Just do a web search using the keywords "E-glass fiberglass".