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.