Two strips of velcro on the sides will keep it from bouncing- the other strips will protect the paint on the vent.<img src=http://www.fiberglassrv.com/board/uploads/3e6140b91ec35ac cover 2.jpg/>
Not having the pleasure of an ac, I was curious why you need the metal cover verses the vinyl?
are you going to put a match on the other side for looks?