Funny you should ask. Good question...and important!
I just recently paid a visit to my local RV dealer store and found a bottle
of roof cleaning solution...called RUBBER ROOF CLEANER
(makes sense eh?) by "Protect All". Is a white 32 oz. spray bottle of
solution specifically formulated to work with EPDM rubber roof's. Haven't
used it yet...but it claims to be "easy" to use...simply spray it onto a 2-3
sq. foot section, then sponge this in to activate cleaner and loosen dirt\chalk.
Use rubber gloves with this and maybe use a bristle brush, if needed. Sponge
this section up into a water bucket a few times to clean the sponge, or mop, until it looks clean,
then go on to the next section working towards the ladder.
They say not to let it dribble over the sides but if so merely rinse it quickly with the hose.
This entire process, once dry, should minimize the black streaks that we all see down the sides because there will now be less chalk
from the EPDM roof material. It also states that you may buy a "treatment"
by Protect All which will make the next cleanings less frequent and easier plus offers UV protection to boot.
This stuff wasn't cheap ($14-) and probably could be found on eBay, etc., if you look, which I plan to do next time with some pre-planning. I think I
saw a roof treatment at Walmart beginning of summer by Thetford but last
time I looked they were out?
There it is and sooner or later you will want to do this. I bought my coach
last yr. as a 2011 but understand the previous owner kept it under a tall carport, which helped. Mine sits out during the camping season, thus far,
but I did cover it completely with an ADCO last winter (Ohio!) to help it out
that way. Good luck...and don't drink and clean at the same time while you are up "there" doing the job or you might have more than black streaks dribbling down the sides of your unit! Just sayin'.
Better yet, see if you could talk your DW into doing this instead, but then take her out for a steak dinner and some dancing, at the very least!
Good luck and get crackin'!