EPDM is ethylene propylene diene terpolymer. Essentially, it is a rubberized coating that is applied, as a liquid, over surfaces such as metal and fiberglass roofs. As in the case of my 2015 Georgetown, it is used over the fiberglass roof structure. You can find all you want to know at the company's web site: EPDM Coatings - Liquid EPDM Rubber Roof Coatings For Roof Leaks
. While some forum members recommend treating RV roofs annually with 303 Aerospace Protectant, the EPDM company rep I spoke with today said all they recommend is cleaning with a mild liquid cleanser if and when needed. On the other hand, retail outlets such as Camping World sell cleaner/protectant solutions they recommend for roofs. Is that a sales pitch or something that really needs to be done? IMHO, those are primarily cleaners with a lot of hype.