I have these nifty abs plastic door cards on my pickup, and the only problem with them was the fasteners that were provided with them since they tend to get brittle enough to break after five years or so if I need to remove the door card. I nabbed some nifty reusable clips that push-in/screw out but I still need about a quarter of an inch to get a snug fit. Initially I was thinking about going w/ some rubber washers, then I realized I would like a bit more sound insulation. What is the best and cheapest thin (~1/4") material I could use for sound insulation?