They are caps that fit over the ceiling air vents. They have two main advantages. 1. When stationary you don't have to worry about rain coming in. When traveling you don't have to worry about dust and other stuff being blown in, so you can safely travel with your vents open as far as you wish.
I have two, on on each vent. The one in front, over the living room even has a fan in it. I can control the direction (intake or exhaust) and speed of the fan. It is a 12' fan with about 10 blades. It is much quieter than the fan that was originally in place and which I removed. That fan is still in the back over the bed room and in the bath room. I am too cheap to replace them.
What are MaxxAir caps, Pete?I actually travel with both air vents open. But then I have MaxxAir caps on
Sincerely,
Peter K. Kaiser
Thornhill, Ontario
http://members.home.com/pkaiser