You know... The "In" vent, high on the drivers side, and the "Out" low on the passenger side.
What does everybody do with them?
Instinct tells me that completely air tight is not good. Even with air conditioning.
I guess one could put an operable cover over them on the inside if they wanted to be able to close them off.
My in vent will be over my porta-potty. I'm thinking, exhaust fan.