not long after mine ran out of warranty I found a very similar issue...If I'm understanding your pictures mine was basically in the same area.....mine was in that little short stand off wall that sticks out to the side just behind the passenger side door...right along the bottom.
Mine has upholstered walls just inside the door behind the passenger and driver's seat, with little decorative buttons. These buttons or simple snaps taht pry right off to reveal screws....a few screws and these upholstered panels come off. I found that these walls are plywood and on my passenger side it was rotted.
Traced mine to a poor build at the factory...I'm confident that it had been leaking since the day they drove it out of the factory door. Had a bad seal at the front intersection...corner of the roof membrane, the nose cone, and the side wall. Also the nose cone was cut short and basically had no sealing surface area at all under the corner insert trim.
I only hope that yours isn't as bad as mine was.
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