[TAKPAK]

Also, another thing that can happen is (if you have no other vents open) when you open or close the outer door, it creates air pressure in the trailer that can cause the vent to open up a bit. I have had this happen on both the 5'er and enclosed utility trailers, especially if the vent is "not quite closed" at which case the crank arm is usually a bit on the "sloppy" side.