So the old ones were made of crummy carboard stuff, wrapped with cheap vynle, and had ceased holding up the rear speakers. So I built new ones! 1/2" thick plywood, leftover new carpet, a staple gun, an air powered saw, some outdoor wood sealer, a utility knife, and some self-tapping screws. It pretty much muted all the road noise in the cab, and I have rear speakers again! The bed carpet was all manner of nasty too, and I still had some extra new stuff.