We have a favorite mobile detailing service wash and wax (by hand) the rig whenever we're in Las Cruces, NM (my hometown where we visit my mom and sisters). The prices are excellent and they know what they're doing. In between those times, I will wash the rig myself with carwash detergent, a spray nozzle, and a soft brush on an extending pole. I recently added a large squeegee to my arsenal to dry the sides and large windows so they don't water spot. No need for scaffolding, here - I back the truck up to the front of the trailer, drop the tailgate, and stand in the bed to do the front cap.
Rob