Also, with a vent open in the rear of the motorhome and the dash A/C running in normal mode where outside air is constantly being brought in - not recirculation mode where inside air is constantly used over and over - you are allowing air coming from outside in front of the vehicle to be constantly flowed throughout the motorhome and out the rear vent.
This means your entire motorhome is slowly but surely getting dusty from the constant flow of air from the outside. We keep all of the motorhomes windows and vents closed when traveling to minimize dust in the motorhome and then primarily use the dash A/C in recirculation mode.
Of course the coach's rooftop A/C system only recirculates air, so it doesn't introduce any new dust into the motorhome.
