I never had trouble with the vent while driving, but where I park
the camper it would get dust in the vent when we have strong
winds--pretty common in Boulder.  So I learned to put a cover
on then.  But we have pretty stong sun, too, in Boulder, at
5400 feet, so after a winter the cover would be brittle and
crack, since you need to flex it to get it "on" securely.

Then someone who had a black cover pointed it that it was a
white plastic cover sprayed black.  Voila!  No more UV damage.

I now have a Vitri and so leave the black cover "on" permanently.

Richard