Hi. I don't have a topper now. Don't have a plan to get one for either of my slides for the time being. BUT. I don't imagine that a properly installed and adjusted topper would hurt anything.
I've had to climb the ladder on a couple of trips to clean mine off before heading home. But for now I'm just gonna go with it. I might add though in addition to keeping water and debris off the top of your slide it should also help some at a really hot/sunny campsite by blocking direct sunlight from the roof of the slide itself.
So. Other opinions may vary. I don't have one (a topper). But if I ever did decide to get one I would not be worried about my slide motor.