There are 'waterless' products that do work well. Over the years I have used Dri Wash, No Wet, and am currently using a product developed for the aircraft industry called Wash-Wax All from a company called Aero
Cosmetics. All of the three products mentioned work well but Wash-Wax all is a system which includes a extendable handle with a microfiber mop on the end. It has two sides...wet side, dry side. I can do my entire 42' coach without a ladder.
These products do work if the coach is not nasty or caked with mud, road salt, etc. But if it is just dusty/dirty from travel, you can get the coach clean and leave a wax or polish finish (depending on the product). It is pretty amazing. Some folks also use the big California Duster to keep their coaches clean.
I still do a regular soap/water wash if the coach is really dirty but most times, the dry wash product/s does a nice job.