the cargo cover tethered to the hatch that hides your stuff? Acoustic matting as in dynamat, the heavy Butyl Rubber stuff? I assume you are trying to turn it into a trunk-like box. In that case, I would find another cargo cover and sandwich the dynamat between them.......or put it on top and then cover that with something. Watchout! I'm spit balling, tired and still at work. Weird stuff will ooze out of this brain.