Pretty much any automotive grade paint will work. Of course you will need to sand or scotchbrite the area before hand. If its fiberglass use alcohol to clean with, do not rub back and forth while cleaning, pick up rag and wipe again. (Fiberglass is very prone to static electricity so back and forth movement creates static, alcohol will remove static.)
Prep, prime if any prior paint or gelcoat had been repaired or scratched, seal and then top coat. If base -clear is used you will want to either spray the entire unit with clear or remask and spray clear a little furth past under coats (like a 1/4") . But im really picky about finishes, you could probably spray some krylon, but you have to spray multiple, light coats to prevent runs.
Ive never painted a rv, but lots of cars, trucks, tractors, trailers and even a boat or 2. In my opinion decals would be much, much cheaper and much less labor intensive.