I went to Home Depot (in the roofing section) bought some butyl rubber backed with aluminum--it already had peel and stick adhesive on it, cost about $1.25 per sq foot then topped it off with closed cell foam insulation that had adhesive and aluminum backing, my truck is as quiet as a church mouse and it does not go dumb dumb dumb......cost $2.50 per sq ft total.
http://kieth.smugmug.com/Trucks/66-G...752_U7LmV-A-LB
The insulation was for duct work and the butyl rubber aluminum backed material was for roof repairs around vents.....it worked great and cost a whole lot less.
we even did the inside of the doors
http://kieth.smugmug.com/Trucks/66-G...8_gTsgqzj-A-LB