I park my trailer next to my house where there are trees.. I've been covering it during storage for the last 9 years. Still on the same ADCO cover. It's dirty, but still works fine.
I just covered mine up for the winter this weekend... This was a pic taken a year or so ago just before I uncovered it for the camping season.
My trailer is a 2003, but bought in 2002. I wash the roof once a year, just before I cover it. During the summer when I'm using it, I don't cover it and as long as it does not rain a whole lot, it doesn't get too dirty, and the leafs and pine needles/cones blow off in the wind when it's dry.
Good luck!
Mitch
