If you google “A E Dometic slide topper installation manual” it will bring up all you need to know on releasing and applying tension to your toppers. My toppers are the same as yours and I put new material on last summer. If I remember correctly the spring tension on all A&E toppers is 13 revolutions. If I were you I would release the tension one side at a time counting the turns as you go, this will let you know if they had the correct tension in the first place, if they did then adding a turn or two might help. Good luck and be careful!
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