i agree w/ dan, use Fat Mat or Dynamat along w/ a two sided insulation material, then carpet,even under the seat. W/ the dynamat (which I use) you only need to cover a portion of the body panel to deaden the ''tin'' sound. then cover that inside panel w/ a full covering of double sided foil insulation.
After I cut mine I used furnace tape all around the edges and 3M spray glue if needed on verticle areas. here is a photo of what i speek of. i bought mine at a good flaps rod shop.
dynamat is pricy but it does NOT EMIT a film in your cab !!!!!
that the cheaper sticky back siding/roofing stuff does
http://www.autostyles.com/insulato.htm here is a way to gain more valuable room and storage under the seat
http://s67.photobucket.com/albums/h298/1951otter/?action=view¤t=DSC00492_0008.jpg I have also used two rubber pieces one above and the other below the wooden blocks in the bed.
:confused: the peel and seal stuff when it gets very hot emits a film on the windows per the manufacture.
