No expert here, but here's what I would do:
Make a rectangle out of 2x6 lumber. Make the height be a tight fit between the basement floor (behind the wall) and the basement ceiling. Make the depth be about 1 foot. Then, attach a second 2x6 onto the face of the vertical piece of this rectangle where it butts up against the back of the utility wall.
When putting the mount in, through bolt it to that double 2x6 vertically in 2 to 3 places.
In terms of voiding your warranty, by adding this wooden support bracing behind the utility wall, you should be fine, so long as you dont wreck or penetrate anything on the RV. By penetrate, I mean, when attaching this bracing to the floor, don't run screws so long that you hit a tank or something else. Same for securing at the ceiling. The wood laminated to the ceiling is not too thick, so your fasteners do not need to penetrate that more than an inch.
That's a heavy TV. Be sure to secure it back to the wall with at least 2 buckle straps for travel.
Finally, look at the new TV mounts we use in Cyclone for the basement TV option. The TV stores flat up against the wall, the mount slides out of the bay, then pivots around for viewing. Not sure of the supplier but I know Mor/ryde makes something similar.
Jim