Over time about any slide out will start darkening the carpet at each end. The slides run right on the carpet when extending /retracting and any dirt accumulating on the bottoms transfers to the carpet. The wear strips are just plastic pieces bent to a 90 degree angle that attach to the ends of the slide floor. It's held on by the trim along the bottom exterior wall ... no biggie to install. There are Slideout Slickers you can buy to place under each end before your retract the slides. They give the carpet longer life and eliminate the black marks. Or ... you can make them as well.