I have the Maxx/Air covers on all of my vents (3 total), there were a new addition at the beginning of the camping season last year. I have to admit that I was skeptical at first but I am really impressed at how effectively they block out rain, even when driving. Given that, I wish I would have installed them way sooner. It is really nice to head away from the camper on a bike ride, hike, to the beach, etc and not have to worry about closing everything up before you go in case the weather turns.
1998 Jayco Eagle 302FK (Honda EU3000is)
2016 GMC Sierra Denali 3500HD 4x4 Duramax/Allison
2003 Honda Aquatrax F-12X Turbo