You can tell how thick your roof is by looking up through the sunlight in the bathroom...I'm no expert but I'd say anything 3 inches or thicker would be safe.
I like the Camco Rubber Roof Cleaner and Conditioner. I use it after inspection all of the fixture seals on the roof for any signs of cracks or holes. I always wash the rest of the camper afterwards, too...and don't forget to open the awning(s) for a bit after you're done to dry it out.
Rick & Karen
(Retired USAF, MSgt)
5-year Travel Trailer RVers
2013 Forest River Rockwood Ultra-Lite 2904SS
2014 Toyota Tundra Maxcrew SR-5 TRD 4x4