I have to agree with LongBox here. Dynamat is the way to go!
http://www.dynamat.com/index.html They have several different types of heat/sound insulation, all geared towards automotive, to include interior and exterior use. Most all of it is self-adhesive (peel & stick), as well.
Just one little drawback; the stuff's not cheap. To do your cab's door panels (best to remove the window regulators and apply it directly to the inside of the doorskin), firewall, floor, roof, hood and back panel, you're probably looking at $500 or more. But it works and works better than anything else I've seen or tried.
Did a VW Squareback a few years ago, and used all Dynamat products to insulate it. Inside, with the widows up, you couldn't hear that thing run at any speed. Had to glance at the tach or speedo to know it was moving! Mind you, the car's owner invested close to forty thousand in that thing besides, so the extra grand or so in insulation and whatnot was more than called for.
