Black Streaks

Thanks for the replies, I would get a lot of black streaks off the back of the 5th/w. The back of the unit is fiber glass and it goes over the top about 12" an the rubber roof meets On the fiberglass part I put a piece of J molding that you use when they do vinyl siding i put it down with heavy duty double stick tape now no more streaks down the back of the unit. The J molding passage the edge of the side about 3" on each side.