I just ran into this same issue I was tired of a metal floor and the associated loudness of the vehicle/ heat and cold. Try this stuff SprayDead Liquid Sound Deadener Documents
I pulled the entire interior and painted on 3 coats and then enameled it all black and put in new carpet.
cot 50 for the spray dead, 25 for the paint from Sherwin Williams 100 for Ebay 7 piece black carpet
it is far quieter and a lot nicer inside now, it is also a lot easier to wash out after mudding because I used black high gloss enamel paint nothing sticks to it
These pics are the spray dead before painting...