Operating the s/o with the trailer slightly out of level should not cause a problem. Sometimes when we stop at a roadside rest area for lunch, the parking area is not that level and we still open the s/o. We have had s/o toppers on all of our trailers. In hot weather, they keep the trailer cooler. They also keep most leaves and other debris off the s/o roof and minimize the risk of water leaks. However they also collect rain water and sag. In a dry climate and when the s/o is closed every few days or weeks, the excess water evaporates or the water and leaves fall off when the s/o is closed. Also the topper fabric is not exposed to the weather all the time.
With a permanent trailer, the toppers will not last as long, so they may not be a good choice. With or w/o them you will probably need to climb on the roof at least once a year and clean off any debris. But then the main roof will need annual inspection and maintenance as well.
Texas Baptist Men-Retiree Builders member since '01
13 Silverado 3500HD D/A, 2wd CCSB srw, custom RKI bed
11 Cruiser CF32MK