Originally Posted by Wayne&Sam
Because the cover closes at the slightest drizzle- even dew will close it. Then you have no ventilation.
Exactly. Whoever said "no cover" probably hasn't lived or camped in Texas. I've had to keep my vent open in as much as four inches of overnight rain.
+1 on the Ultrabreeze, for the reasons stated. Installation couldn't be easier. Here's a short blog post that contains instructions.
FANTASTIC VENT COVER INSTALLATION ON AN AIRSTREAM INTERSTATE