Heat & Air Pressure Problem with : OEM Hard-Coat bottom tip-out -- Roof & Hard Kolpin Rear Panel with( P520 DOORS).
Installed Vent in rear panel of Roof. (Pictures)
Towing :
Tip Vent opening to bottom ( downward Air Flow )
All windows & doors Closed does a good job reducing Cab air pressure while Towing.
Reduce Cab Heat :
Tip Vent opening up (upward Air Flow ) & Open Tilt Windshield at Bottom.
Allows decent upward Air Flow & with door windows open -- maintains decent air movement & several degrees cooler.
Not as good as A/C although does make 90° day more comfortable.