We always have windows at least cracked open when camping. Our skylight in the bathroom opens, so I open that about an inch (low enough that rain won't come in) and open one of the windows in the front of the camper about an inch. Usually I can feel a slight draft coming through the window, which is what I want.
Our bathroom skylight also has a Fantastic Fan, which works great for "power venting" our 21ft camper.
Sometimes we do use the A/C fan at night for white noise. Some campgrounds can be noisy until late.
If it is a really warm night and we need to use the A/C overnight, I STILL crack open windows for venting. You need that fresh air!
