John, if you could post a photo or two of the situation it might help us. If you need them, there are "Stickys" at the General Discussion Board about how to post photos.
My units have spacers around the perimeter that were nearly lost awhile back. BCS adjusted the snugness and stabilized the spacers. If your spacers have blown away, that may explain some sag, but like Ed mentions, BCS should have caught such a thing.
-Joel