undercoat floor

I did something similar to this in a 1984 power ram I had. Pulled all the old carpet out, cleaned up all the rust, scuffed up and cleaned the floor. I used a gallon of herculiner roll on bed liner, probably too much but it was fine. Completely sealed the floor. And what was good about it is that you could scrub it clean and rinse it if needed.

As for the cab noise, you could buy a roll of sound Deadening material and put that between the floor and the carpet.