No need to wash the roof, other than to make you feel better. All it does is give the birds a cleaner target to aim for or make your trailer look a little bit better on Google Earth. Doesn't help the roof, doesn't make it last longer, doesn't prevent black streaks.
Roof conditioner is a scam to make you spend money. The manufacturer doesn't recommend any conditioners. Some people started looking for products to put on their roof to make themselves feel better, so the manufacturer created a product to fill that void. It doesn't extend your roof life and doesn't help with black streaks. All it does it put more money in the pockets of a chemical company somewhere. If it makes you feel better, pick any roof conditioner at random and spray/wipe it on.
Inspect the seams and make sure the caulk is in good order. I just use Eternabond tape. Install it correctly once and you are good for the life of the trailer (or 20 years, whatever comes first). Get on your roof once a year and inspect and you are done.
Like wildtoad said, put a piece of Eternabond tape under the antenna where its rubbing, that will solve your problem for a long time.