Floor insulation pad??

[swamp rat]

I need to find a good quality sound deadening and insulation pad for my truck. I replaced the rubber floor mat about 10 years ago but didn't buy an underlayment pad, I used some cheep crap that I had at home to save money, as you may emgen its rather loud inside the cab with all the engine, exhaust and road noise.

I don't want to install any of the stick on dynomat or brush on stuff because i'm still wanting to do a frame off (someday) and have the cab sent out to be tanked to kill any rust.

I need something for under the floor mat, but also need something that will lay inder the the seat as well.

Is there any type of matt that I can buy to lay against the rear of the cab behind the tank?

Any advice or recomendations would be appreciated