We are on the road all the time, we have no residence. Most RV parks will not let you wash your RV. I have used truck stops that charge from 75 to 125 dollars and do a terrible job. What do most do?
The campground we stay at snowbirding doesn't mind if the long-term folks wash their rig within reason. That said, if it rains while we're traveling, I take out a brush and wash away. In addition, many campgrounds will let you wash your rig for a $5 charge. Camp on!