Ha! Ha! Yep . . . trash bags. I just used black duct tape and taped the trash bags up long ways across the windows, along with a couple of black shoe strings taped strategically along the way to use as tie-backs. They work perfectly and cost next to nothing.
Here's a pic of how I can use an Army-issued mosquito net to drape over the back of the camper when it is open. Air comes in but bugs stay out.
and I just had to put one more pic of the shelving unit that fits so perfectly in one corner. This gives so much accesible storage space and I use a couple of bungee cords to keep the drawers secure while the truck is moving.