We have a 2015 29P RKS and I have mounted a 40" flat screen in the entertainment space for a TV, NOT the bedroom. Following the above advice for pressing to feel stiffness in the trim panel showing factory backer, I then screwed a 1/2" piece of plywood that was twice the TV wall mounting plate in width and height, and then screwed the mounting plate female receiver to this. My hardest problem was measuring the install height of the female receiver plate to correctly center the TV within the box opening.
Have over 4000 miles with this and no shift or looseness to the TV, combined on highway and back country dirt roads, as our trailer is base camp for horse showing.
My use of the extra plywood is probably overkill, but I'm a belt and suspenders type.
Fx