I very seldom use water to wash my coach. I dry wash it most of the time unless it has been through a storm and is full of mud. But if it is just dusty I use The Solution and it preserves your full body paint job with UV protection and at the same time it polishes the coach.
Now on the roof which is fiberglass, about every six months I get up there and I wash it real good with water and a mixture of Blue Coral wax. I just apply it with a mop and it will also protect the fiberglass from UV rays. The wax on the roof is more for protection of the sun then for shine.