All keep in mind that slide toppers are not designed to keep water from accumulating on top of the slide itself, but only to keep debris off of them.
I think slid room roofs should have a slight hump in the middle as part of their design, so that water can drain off either end. Contrary to my design beliefs, it seems that many actually have a dip in the middle for pooling and holding water. Not only that, but to the point of retaining it and even with the slide being retracted and going past the top seals. Just don't get it and never gave it much thought before, since our old tropical has never done that..