Monaco products, model years 2000 to sometime in the teens, can have the "beltrail" joint loosen. The "beltrail" joint is the one between the sidewall and the roof (although at the ends the front and rear caps are included). On the passenger side that joint is behind the awning rail.
What typically happens is water enters the beltrail cover and rusts out the screws that go through the joint. The screws fail as the coach flexes, allowing water inside the wall.
I would examine the beltrail on both sides. Look for places where the cover is popping loose. Our coach's beltrail failure had two symptoms: 1) a leak in the front passenger window area, and 2) a sharp popping sound above the entry door when getting underway (from having been on the levelers).
Another source of structural distortion could be from the frame and suspension. I have read of broken welds causing frame/suspension members to shift out of position. It probably would be worthwhile to have a shop look under your coach, if that's work you wouldn't usually do.
These are "shots in the dark," and probably don't apply to your situation, but you never know.
2008 Holiday Rambler Admiral 30PDD (Ford F-53 chassis)
2009 Honda Fit Sport