Roof vent lid gone... how did this happen?

Before I put a cover on, I had a vent lid vibrate itself open one day as I was towing it into a fairly strong headwind going across Montana. I stopped for lunch and found it raised about an inch, not enough to rip off, but enough to set me wondering. I cranked it down, made sure it was tight, and a couple hours later when I stopped for diesel, it was back up. I can see, if the wind is strong enough, and long enough, how it would crank itself open enough to tear off. I think that review of those security tapes are going to be the only way to find out the truth.

So here's another vote for one of those covers. They not only keep your vent lid safe from the winds -- and thieves -- they also make it possible to keep that vent open during a rainstorm.