We spend a lot of time on dirt roads, and dust infiltration has been our most serious problem. I have caulked and sealed everywhere but dust still gets in, primarily at the bottom of the (rear) entry...
Could try positive cabin pressure. It might not be powerful enough to overcome dust while driving. But it could help if you camp in dusty areas.
I installed a 4" marine bilge blower under my trailer. With a 4" automotive air filter on the intake. The air travels through 4" plumbing pipe into the trailer and is controlled by a PWM motor controller.