When I did mine I first made a plywood insert for the hole and then bought a 4x8 sheet of fiberglass... shower wall material. Removed the aluminum trim and ran two strips of 3M UHB tape along the top and sides and four strips on the nose bend. The fiberglass had no problems bending around the nose. Once the tape made contact it held. You can then replace the trim or what I did was lay down 6" and then 4" fiberglass tape using marine epoxy resin. Worked out so well I eventually replace all the trim on the RV the same way.
