Do you have an L Square?
With the door open place the long end on the side of the door frame and the short end on the door threshold, hold the long end tight to the frame side and check the gap at the threshold hooked and unhooked.
The difference between hooked and unhooked will tell how much flexing the door frame is doing.
Check the screws or rivets that hold the door frame to the trailer floor and walls.
2016 F350 6.7L LB CC Reese 28K 2014 Chaparral Lite 266sab
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