I just finished cleaning my epdm roof and dewinterizing the HTT.
The epdm roof manufacturers recommend cleaning and conditioning your roof twice a year
Having purchased my HTT in June of 2010, I never got to cleaning the roof at the end of the season, due to the change of cold and wet weather early in the fall.

So I decided to clean the roof before we go camping April 15th. Having everything ready, ladders, brushes, cloths, bucket, hoses and roof cleaner (Thetford Premium rubber roof cleaner and conditioner). It's important to purchase a roof cleaner that has a conditioner as it helps the roof remain pliable. Roof cleaners that don't have the conditioner may dry out your roof.
I inspected the roof and caulking and found it in decent shape. However, since I didn't wash it last season the epdm had a number of stains that took a while to cleanup. Especially under the antenna where the aluminum stained the roof. That can't be good for it long term. There was also staining along the A/C and roof vents.
It took me about two and a half hours mostly using the long handled brush I had, but also hand scrubbing. You can't do a very large section at a time when you are on an eight foot ladder.
This is not an easy task and certainly not one the RV dealers mention often.
Also very important to do since you can't see branches, etc that fall on your roof and may do damage. Better to catch any penetrations of the roof early, so they can be repaired before you get more expensive damage,

It should also cut down quite a bit on the HTT side wall staining since the roof is clean.

This year I will plan to do the 2nd. roof cleaning late August or early September and start it all over again next Spring.