Side wall has separated from horizontal frame structure.
The side wall sits down on top of horizontal frame and is bolted to it with lag screws. They pull loose or break.
Then when you hitch up pin box structure lifts side wall before it starts lifting horizontal frame.
When unhitch and landing gear carrying weight, side wall settles back down onto horizontal frame
Caulking is NOT going to work..will just continue to pull loose/gap
New lag bolts can be install thru side of horizontal frame into side wall bottom plate. Drill holes in a 'W' pattern. Use 1/2" X 2 1/2" lag screws.
Also add couple up thru bottom plate.
OR''
Side wall stud welds on bottom plate have broken.......then you need to remove side wall and re-weld
OR'''
Pin box structure has cracks/broken welds/torn metal..re-weld/add braces/supports
You will need to remove overhang panel and inspect frame structure.
Hitch-up and unhitch to locate issue.