I don't believe there is any way to really clean a coach (or car for that matter) without touching it with something. Even pressure washers don't get all the stuff off.
I wash my coach with a 'Swobbit' which is a soft, fake lambs wool pad on the end of an extendable pole. It gets the job done without scratching the clear coat finish. I wash with Turtle Wax Zip Wash.
When the coach is not really grimey but mostly dusty, I use a waterless product called Wash Wax All. It really works well. You spray a light mist on the coach and wipe it with a special micro fiber mop that has a wet and dry side. Or, you can use micro fiber cloths. It really does get the dirt off and leaves a nice shine. It was developed for cleaning aircraft.
There are other waterless products that work such as No Wet and Dri Wash.