I had owned this coach since 2008 and had washed ~2 times a year with car wash soap but it kept getting dirtier and dirtier.
Last ~June I finally bit the bullet and started scrubbing with a combination of Awesome, Tide, and Soft Scrub on my hands and knees with a hard bristle brush. I also used a small pressure washer to get it completely clean. The hard work paid off and it was as white as when it came out of the factory. I then put ~3 coats of Zep high traffic commercial floor wax on it. Below is a picture after this was done.
We did a 2800 mile trip and then I rewashed the roof in Oct and all the dirt that had accumulated came right off. I looked at the roof today, after another ~1500 mile trip in December and the roof looked nice and shiny white.
2002 Monaco Windsor 38 PKD
2005 Jeep Grand Cherokee w/5.7 Hemi