Are you able to drive with the vents open with MaxxAir vent covers?
Yes. We even can leave a vent open all year with them (though if snow starts getting deep we do shut it, not wanting melting snow to leak in.) Some trailer vents will shut by themselves while driving, though - I think it just has to do with airflow. In our last TT we had all 3 vents covered with MaxxAirs, with Fantastic Fans in 2 of them. One of the fan ones almost always would close when we were underway, but the other 2 remained open. Never had a rain leak, even in heavy rainstorms.
We have one black & one white on our new TT. Looks a little funny, but we always seem to land the spot in the CG right under a street light :R so I asked for a dark one over the bedroom this time. Hope it helps. (New TT so we haven't camped in it yet.)