Russ,
We have traveled full time for five years with two cats in a large Class A. While we do let the cats find their way in the coach as we travel, typically they prefer to park after the initial half hour and sleep.
That said, we have had issues with them roaming and getting into the driver space and they are unpredictable when they do that. It's a huge distraction and dangerous. Are you going to step on your cat or the brake? As you shoo them away, how distracted are you?
Giving them an open window, even with a mesh, does not sound like a great solution, especially if you are the only occupant of the coach.
You may have a different experience with your cats and this advice would not apply to you but this is our experience.
Kim