I wash my TT at campgrounds, more often than when home, and it doesn't matter if the campground has a no-wash policy or not.
I simply do small areas at a time with a bucket and sponge, and rinse with a sponge and dry with a soft towel. Sure, it may take a few days to go all around the camper, doing it this way in 5-7 foot section at a time. But the pay off is, no one will question you, since you're not dragging out hoses and your not soaking the ground or camp spot.
Last Summer, we took a week trip, staying at 3 different campgrounds. I was able to wash the camper at home, (all at one time), but spent the entire next week camping, spending about 30 minutes each day, to go over a small portion of the camper, wipe it down with a clean cloth, and then wax that portion. When I got home, the camper looked fabulous.
If you wash small areas at a time, and do it consistently, you'll never have to pay anyone or hire anyone, or be concerned how you're going to get it clean. It only takes 30 minutes a day or less, but it does take a certain commitment to stick with it.
Once clean, keep repeating, and you'll never have a dirty camper.