I have seen a few trucks with inserts for the rear windows that were not chrome. I have never known if they had chrome at one time and someone replaced it with a rubber one like the windshield, or if some gaskets had the plain black rubber insert. Had a glass guy tell me years ago its caller a zipper! You will want to use a spray bottle with dish soap and water mixture for the rubber when you install it. Also over lap the rope on the bottom, and pull the top one out first. Set the bottom rubber in so the rope doesn't really do allot. In other words place the gasket so its somewhat in place. As you work your way around have the person on the out side apply moderate pressure right about where the rope is coming out of the gasket. Also keep a bit of pressure down to keep the bottom of the gasket somewhat seated. I use a little masking tape to keep the ends of the rope out of the way, tape to the glass. Small non nylon cloths line rope works good, 1/4" or so.