Originally Posted by family wagon
... ... But are there high- or low-pressure zones that develop because the vehicle is in motion?... ...
Yes! And they are strong forces indeed.
You probably ought to research this quite thoroughly. I imagine there is plenty info online, but it may take a lot to time to find it.
I know a little bit: On the sides and roof close to the front, there is low pressure. This is from sort'of a venturi effect, caused by all the air hitting the front of the bus and being forced outward at high speed. Or maybe a sort'of back eddy effect.
You can confirm this yourself: Open the driver's window and toss some scraps of tissue paper around. They will blow OUT the window.
In Millicent we have a problem with exhaust fumes in the front of the bus. The air that is "sucked" out of the front area must of course be replaced, and that air comes from the rear, where exhaust fumes are drawn in.
Millicent has a wall with a door across the middle, separating the "residential" and "cargo" areas. There is a one inch gap under that door. We have learned to stuff an old towel under that door, to reduce exhaust fumes up front.
How does all this exhaust get in? Well, that's my fault. The "toy hauler" tailgate is not exactly airtight. So I need to work on that too.
(Mind you, this exhaust problem is not enough for me to even notice. But some of our passengers are more sensitive.)
Now...: Last year I cut a 12 inch hole and installed an electric fan in the wall between the bathroom and the cargo area. This is specifically for camping in a hot desert, when the bathroom can become awful hot.
Guess what.... On the road, airflow from the cargo area into the bathroom spins that fan backward like gangbusters. The bathroom door is almost difficult to close against that air flow!
So I have a ton of research and experimenting to do on this.