rubber roof treatment

Clean roof first with about a quart of Clorox and some soap in a bucket of water. Use a long handled bristle brush. Wet roof first, then scrub and let Clorox kill all mold, then rinse well, let dry or dry with leaf blower. Then apply roof caulk on open joints and then mop liquid roof sealer on. That process needs to be done every year as the road vibration and weather loosens sealed areas and water then gets in and damages frame and mold sets in.

It depends on how good a job you want.

There are lots of diy methods of coating your roof.
I've done two lately and results were very good.
Clean first, calk then apply coating.

I'd also consider Eternabond. It isn't a cure-all, and needs some prep work (clean the roof with acetone or another solvent before applying, then use a clear caulk like EternaCaulk to keep dirt from adhering to the tape's edges after applying and pressing into place with a roller), but it does have a very good record (few complaints on the forums.)