I wax the top too. I work off of a high "A" frame style ladder and stretch to reach as much as possible and go all around the trailer. I found that I don't have to crawl on top. When doing the front, I lower the jack. When doing the back I raise the jack. The in between works out and I am able to get it all.
Some use scaffolding for repairs and you could also use it for any roof top jobs including waxing it.
"Thereís two kinds of people, them goiní somewhere and them goiní nowhere. Andís that whatís true". -Ben Rumson