I have seen some people that use a beach ball, but they have a long string that attaches to the ball, goes across the top of the topper, hangs down, and then up the other end of the topper and back to the ball in a continuous loop.
When you are leaving, you pull the ball out from under the slide from one end of the loop, and set the line on the slide roof next to the outside wall, then let the slide in. The two cords hang down and the ball and extra line tucks into a storage locker.
Once you are parked, take the ball out of the locker, inflate it, and feed it back in again with the continuous loop line.