What Blaster Man said X2.
my RV is also under pine trees. the roof and slide topper ARE covered with black sappy mildew. It is hard to clean, almost impossible. But who cares?
I covered mine twice. I probably won't cover again. The wind is tearing the cover in places since my 34' rig is 4' short of using the entire length, so on windy days and nights there is lots of slack flopping despite all my efforts. even the tied-down bottom sides are ripping at the grommets.
Pulling that heavy monstrous thing up and over is dangerous! too many expensive things to step on/through or trip over, and an 11' drop to concrete if I go over.
Not worth it in my neck of the woods in my opinion. Wind and Sun are the problems here. Go for a rigid cover if possible.
PM me if in my area and I'll make you a race-horse deal on a BIG cover! B+ condition.