sark
42601-60262-03
Most arches I've seen non-stock are sound-matted and then covered with either the OEM arch fabric or cut-your-own style and tucked under the regular floor carpet. I saw this liquid sound deadener recently that you could try to paint over with: Spectrum™ Sludge Deadener - https://www.secondskinaudio.com/sound-deadening/spectrum-sludge