If you will make sure the roof is treated with Protect-All Rubber roof solution , clean the trailerwith RV wash, wash the black streaks with "black streak remover" from Walleys or any RV dealer, clip a clothes pin on the gutter outlet spout, your trouble will be greatly reduced. Long sentence huh? You can not let it get ahead of you and try to catch up. You will lose.
Also I wax my 32 footer with Gel Gloss. A little work but great results.
. . Preston. .