I do it myself in the campgrounds with the little "lunchbox" pressure washer I carry and a foam cannon. And one time at a harvest host in Iowa (great guy). He had two full hookup spots put in by his shop because he wanted a place to dump his rig and also make friends from harvest host!
This is the little guy I carry with us for the truck and RV:
Pressure washer
Whenever we pull into a campground, I keep an eye out to see if anyone is washing so I can put that task on the list while we are there. It gets done about once a year. 6 months of that is usually "man I really need to wash this thing" until I actually get around to it (still work full time on the road). Last time it got washed for the 4-5 hours it takes me, our next stop was an overnight boondocking spot up like a 6-mile switch back dirt road in CO that got it all dusty again...