I think the problem you mention is while you are parked. Or is it while travelling on the open road? Even travelling through dusty areas with the wind blowing farming dust off the fields is a problem hard to control.
There are a lot of leaks on any RV that allow dust, rain, critters, etc. in so the task is to eliminate as many of the obvious openings as possible.
If this is happening while parked, the key is to try to pressurize your unit so that dust does not enter. Using the air conditioner or furnace, does not bring in much outside air but only recirculates inside air. You will need some type of fan drawing filtered outside air in to help pressurize your unit.
(This might be your opportunity to invent something along this line?) 
Pulling a trailer behind a tow vehicle will also present a challenge to control dust. On a motorhome, one has the ability to draw cleaner fresh filtered air in to try to pressurize the unit on dusty roads, but this is not possible with the trailer.
Years ago, with SOB camper, we had to overnight on the open prairie in northern Alberta during a heavy wind storm. It was cool, so we had no vents open, but the next morning, the camper and everything within, was filled with prairie dust.
My DAD had a 41 Plymouth on the farm that had a number of rust holes in the floor and wheelwells. The trick to control dust on the dirt country roads was to roll up the windows and turn on the heater blower to high. It did work. (the old cars used to also have a cowl vent to help control this problem)
Dave
Best way to control dust in Air Stream
Linear Mode
