TV Mount

[MSSauter]

Greetings. I have a 212FB model. I want to install a swing arm TV mount in the TV area above the sound bar. Using two different stud finders, I can't find a solid surface behind the facing wall, and the side of the "box" seems hollow as well. A video I found of the model looks like the factory installation of a similar mount used an additional board run vertically on the left edge of the TV mount area. Has anyone else tried installing a mount in their trailer? Any suggestions would be much appreciated.