FYI - 2012 X-UDS If you ever leave the damper open on the exterior of the range/stove exhaust vent, it will vibrate and fall off while towing.
One fix - simply replace the damper door. It has the two small "nubs" at the top, one on each side. A replacement door can be flexed and fit in.
You may somehow scrape the side of the trailer and damage the vent itself. The vent with damper door can be removed and replaced.
The link is one possible source for the vent/damper door assembly. I think you can buy the damper door by itself. I haven't found a source yet.
One of the more popular vent makers Ventline will not fit.