Done a 46 twenty five years ago that is still cooling great at 55mph. 65-70mph and the cool all gets sucked out of the cab. First two things done was to seal the swing out windshield and cowl vent PERMANENTLY. With heat, a/c, and side windows you don't need them. They leak water so they darn sure leak air. Used stick on mat for sound only and covered it with the bubble foil for good heat insolation. You can hold the back of your hand against the firewall or trans tunnel and not feel a change in heat from other cab parts. The bubble foil also was used on the roof, cab back, inside of doors, and in the kick panels as well as the floor and firewall.
