That moisture barrier you made looks good - a nice neat job. Also, in addition to acting as a moisture barrier, it will likely make a significant difference in the degree of noise & heat transfer through the door.
HKJ's observation - about the doors playing an important role in cab ventilation - is correct. But given the way you sized/located the barrier, it won't have any impact on ventilation.
The heat/AC blower is always drawing in fresh air from the outside and discharging it into the cabin. Even when in MAX AC mode, only 90% of the incoming air is recirculated. The fresh air inlet damper under the cowling is designed so that it can't completely close and that opening supplies the remaining 10%. So (if we disregard MAX AC mode), whatever volume of air that comes out of your dash/heater/defrost vents is is equivalent to the volume of fresh air drawn in from outside. For the HVAC system to work as designed, the cab must have exhaust vents of sufficient capacity to accommodate the volume of fresh air that is flowing into the cab. It's not the same air - the new fresh air comes in and pushes the old stale air out -
In theory, if all the seams and weather stripping throughout the cab are factory tight, the only
