I send my 9 year old up there with a car washing pole and brush. I tie a rope on the bucket with some soapy water and "direct" him. Wax on Wax Off. We do this every time we get back from camping. The more you do it the easier it is to get clean. It also gives you the opportunity to inspect the roof. I noticed a crack in our skylight a few months back, which was a good thing before the rainy season.
2007 20BH Jayco JayFlight
2009 F150 5.4L SCrew Cab XLT