Home Depot has a product called Zep I use in rental bathrooms to get ride of the mold when I replace the caulking. There are two products that I use in the Zep line one is a mold killed and the other is a soap scum cleaner both work well and are CHEAP. Like $3-$4 a bottle, spray on and wash off. I would test on a small hid area so if discolor would happen but I think 'on the directions.
I've had good luck using an SOS pad, scrubbing lightly so as not to chew up the rubber. When I bought my trailer, it was sitting for a few years and the moldings were pretty bad in spots now, just washing it a couple of times a year seems to keep the problem in check. Some of the new trailers I've looked at have are using black moldings instead of white which seems like a good idea to me.