For routine cleaning, I use Thetford Rubber Roof Cleaner & Conditioner. I use that on it 3 to 4 times a year.
For heavy mildew stains (I've only had to deal with it once, on this used Cruiser I have now, when I bought it), Tilex Mold and Mildew Remover works wonders. It took 6 bottles, about 4 hours, and a lot of elbow grease, but I got that roof looking great. A word of caution is to liberally keep the sides washed down to prevent the bleach streaking your paint and decals.
Mike in Tennessee
Former 2 time FR owner
2007 Crossroads Cruiser 30QB Fifth Wheel
2008 F-250 Lariat 4x4 6.4 Powerstroke
Firestone Ride-Rites w/cab control