Fiberglas side walls?
NuFinish is real popular and seems to be long lasting.
Lately on my car I have been using Mcguires Advanced polymer polish. Super easy on/off and seems to last. How often depends on too many factors. On my fiver I uusally waxed it once a year in the spring. Then I was using Mcguires RV/Marine line with excellent results. I also have used and really liked Colinite fleetwax, which was designed for aircraft.