You have the right idea of treating the problem instead of the symptoms. The problem is the vacuum of the dead space behind the camper drawing the dust in to the back wall.
Bear with me I'm thinking outside of the box here.
You might try adding a small "wing" at the top of the camper to direct wind into the void. I would do a test with some clamps and maybe a 1" x 6" board. Run it all the way across the very rear of the camper at maybe a 45 degree angle with the forward edge up. That should disturb the vacuum enough to keep the dirt off the back wall.