Is there anyway to have AC power while journeying? If so, you could have a vacuum cleaner with a HEPA filter running while traveling. Better yet, if it was a canister vacuum such as a Filter Queen, you could have the suction hose some how sucking outside air. I mention the Filter Queen because it as 3 stages of filtration and still moves a lot of air. They are expensive but seem to last forever. Mine is over 20 years old. They can sometimes be found used very reasonable. We sometimes run ours not vacuuming but just to freshen up the room air.
