I guess others here don't use covers
. I personally wouldn't encourage the use of a tarp, but I would support use of a breatheable RV cover. I have used one that has a tarp material on top and on the ends, but a breatheable material on the sides. If you choose to keep it uncovered, make sure you clean the roof VERY often. I think a cover would be a better use of your time- take it off and go. That way, you wouldn't have to make a point of cleaning the roof all the time.
Hopefully others will offer their opinions!
2007 T-286SR Cherry/Granola, #6236, original owner, current mileage: 9467.8 (as of 5/26/19)
1997 T-2653 Blue Denim, #5471
1979 12 1/2' MC, Beige & Avocado, #4639
Past Sunlines: '97 T-2653 #5089, '94 T-2251, '86 T-1550, '94 T-2363, '98 T-270SR