How to wash and wax/polish a Class C/fiberglass exterior

NEVER EVER pressure wash an RV. Not only can as you discovered strip the wax. It can be far more damaging force high pressure water past seals and into or between the walls.
Get a long handled csr wash brush and a bottle of car wash soap. Wash starting at the top and work down. If its fiberglas exterior then products like McGuires RV/Marine products in the blue bottles. You have lots of boats jp there, stop in a boat store and ask them what they use. It takes time to do right.