cost me 22 quid fer enough underlay to do it about 20 times n i kept me living room carpet when a changed it ifit gets soaked or manky i jist replca ituntil yu get it wet - and it rots ya floor like buggery.
cheers red.
works great inside door panels and under bonnet, you aint gonna get no water trapped behind it either, reflective on one side for noise, and being rubber its takes away some of the vibration.
no cheap, but cheap enough.
instant landy soundproofing, only £4.99
http://i138.photobucket.com/albums/q244/yella-fella/****e/4.jpg