Like Howard said, pitch can have a lot to do with it. A lot of the new fivers have taller slides for headroom, but it takes away from the space above the slide to mount the topper rail which reduces pitch.
This can stretch in the middle and then they won't roll up correct, or nice. After one year, a few of the folks on our forum have had to replace the fabric because of stretch and will have to go with some other inflatable contraption underneath to topper to keep it from happening again.
Just make sure you have the full clearance you need to the roof, and then some. I didn't order them and have never had them, but might if we lived in the east like you.