Not a Fifth wheel and we have awnings or toppers, still dirt etc gets on the slide room tops.A step ladder and either the long arm squeegie or the wash brush and old small wet towels a from each end after using a hose on them with the front jacks up a bit higher than the rear. I've contemplated buying a broom handle or something else as long as I can find and using a piece of hose to join it to the long handled wash brush, Or main slide without looking it up or measuring looks like it is 18-20 ft long.Its a chore to clean the top. When they are in I have small limited access over the inside edge and have put a loop of twine knoted on each end of a wet towel and drug it back and forth too.
A full wall slide would be a real challenge. I face cleaning the room tops when we pull up here as we have set here in the desert with lots of very fine dust.
I may try the sacrificial towel and twine or small diameter cord dragging it back and forth rinsing in between trip on the outside top before bringing them in.