When we camped with the van and a tent that hooked up to the van I fashioned screens for the car doors by just folding over
fiberglass screen and stiching the sides like a pocket. This would slip over the top of the door and cover the window. Some of those rubber magnet strips that car signs are made of sealed the outside to the car.
This worked well for years, keeping out all the nasty bugs and letting in gobs of fresh air.
Screening can be gotten at any home depot, etc.