I attended a seminar on this topic at a FMCA rally done by professionals.
They suggested having a pump sprayer filled with water and a small amount of dishwasher anti-spot liquid mixed in. After wash and rinse, spray the solution on the coach then rinse again, then wrap a microfiber towel around a window squeegee on a pole and dry the RV off.
It works great. No spots at all, looks like it was just waxed.