Naio, in 1976 I went on a binge. Yanked the seat out of my 1970 chevy pickup. Padded the floor with closed loop nylon carpet. Drilled holes in the overhead and fill it with aerosol foam. Took the doors apart and laid 1" insulation on the inside of the exterior sheet metal then that sticky brown sound absorber factory stuff on the inside of the interior door sheet metal. An upholstery shop redid the seat. Carpet was glued to the behind the seat gas tank which was removed and insulation stuffed on the rear cab wall.
The difference was astonishing. We had days of 0F fog and before the defroster kept a dinner plate size hole of the windshield defrosted, afterward in even colder weather not only was the whole windshield defrosted but I had to turn the heat down.
The truck was quieter than my 67 caddy. I could park in subzero F and the truck would take 20 minutes to cool down in the cab. Summer 100F temperatures were throttled by cutout shades on the windows when parked in the sun.
All this made a lasting impression on me.