Keep in mind that the ZEP recommendations here are for "Molded Fiberglass" applications and may or may not work well on the sheet fiberglass
your RV usually has. I'd try a small area first, like a baggage door. And it will take 4-6 coats.
Good luck and let us know how it comes out.
That said, be sure to clean it like crazy first, ya gotta get all the dirt and oxidation off, a sometimes killer job, even on our little ones.....