I would imagine that following the manual that came with your trailer would be a good way to go. Here is a quote from the section in my owners manual about caring for rubber roof:
"The rubber roof is a polymer membrane that will not rust or corrode and is very strong and durable. Other than periodic washing, the rubber roof material itself does not require maintenance or coatings. However, be advised that any attachment, seams, or joints in the rubber roof requires maintenance often!
The roof material can, however, be punctured, snagged or cut by contact with other objects. Know the height of your unit and avoid contact with overpasses, trees, ectc. If the rubber roof is damaged, it is designed to be patched. Rubber roof patch kits are available through your local dealer. If done correctly, these kits are designed extremely reliable"
On my trailer, the roof is partially visible from the ground and when it is dirty, it spoils the looks. I will clean it once per year.
