The heat shield recommendation from Flowmaster, is more of a safety note than a fix for heat transfer to the inside. If you are using a rubber mat or carpet in the back, use a hot water heater blanket that you can purchase at most hardware/Home Depot stores. Very easy to cut to fit. Place the foil side down and matting side up. Use spray adhesive to hold it in place, and just install your mat or carpet over the top. Works great!