Our toppers are made by Carefree, and their tension is adjustable, BUT when I looked into tightening one of them up (just a little) it looked like it would be very easy to screw up, and then the tensioning system could unwind. It's been awhile since I looked at it, so I don't remember all the steps (I downloaded them from Carefree) but I seem to remember that (at the time) I felt it was a two man job.
Kev