I imagine the OP is using an RV type roof cleaner and an RV type conditioner. If you are, you're doing well once or twice a year at most. I use only RV cleaner and conditioner. I wash the roof, usually in the early Spring and go ahead an use the conditioner at that time. If I begin to notice black streaks forming on the sides too much, I'll then wash the roof again, usually by August or early September. If washing, I always use the conditioner.
There are some that say it's OK to to use bleach, Spic-n-Span, all sorts of stuff. For me, using the cheaper cleaning solutions is not something I want to take a risk on, in the long term, deteriorating the roof. But RV roof cleaner and conditioners are designed for the rubber roof. I don't mind paying the little extra for the correct cleaning solutions. I've NEVER had to caulk anything on my roof, on 3 different travel trailers because the caulking was deteriorating and cracking, NEVER! .... I think the reason so many folks have to recaulk so much is because of using harsh cleaners! That's something to think about. So if you are using the RV cleaner, go ahead and use the RV Conditioner every time you wash. It's an extra step, but well worth it in long long. If you wash once a year, use the conditioner once a year. If you wash twice a year, use the conditioner twice a year. Basically, every time you wash, use the conditioner. It will keep the rubber roof healthy, and will also help the areas where caulking is.
