[jetskier]

To further elaborate on my previous post...the reason the studs are breaking there is the re-entrant vertical force on the aluminum wall stud caused by the discontinuity of the wall panel at this location. Even though this is not a place of maximum moment in the frame, there is upward curvature in the steel frame when the trailer is hitched up. The measured relative deflection at the front of the slide opening from this curvature creates a force that is too much for the aluminum stud framing and it's connection to resist. After many fatigue cycles, the aluminum fractures and busts out the siding panel. Having a continuous horizontal framing member in the wall panel below the slide accomplishes a few things. 1) It provides a boundary member on the bottom of the slide opening to resist moments, shears and deflection, 2) it removes the re-entrant forces at the lower front corner and 3) it provides more length to make the connection of the wall to the frame at the slide. This is likely the reason for the 2020 design change under the slide.

And yes, if you haven't figured it out, I am a structural engineer.