Two options come to mind...
Have you considered a pipe-style mount? Take a pipe stand similar to this
https://www.amazon.com/gp/aw/d/B001F...=tv+pipe+stand
Take two 4” x 3/4” pieces of red oak, cut 1-1/2” holes in the middle of them and put a decorative edge cut in them. Cut the tv stand pipe slightly shorter than the distance between the upper and lower cabinet. Slip the oak squares over the pipe and position on the cabinets nice and vertical. Mark and remove for now. Drill a 1” hole in the lower and/or upper cabinet to chase wires from the cabinets through the pipe to the back of the tv. Bring the pipe and oak pieces back and mount them securely either with screws from the cabinet side so they don’t show, or something decorative if they do.
They make tv mounts that will bolt directly to this, and you can then twist the pipe for viewing in either space in the trailer. DVD, satellite, etc can go in the cabinets with no loose wires.
Downside - it eats the countertop space.
The weight is on the lower cabinet with this design. No attachment to the exterior. Permanent damage to the countertop, but replaceable. Easily available and common components.
Just thinking some more...I’d want a better friction surface on the lower end of the pipe to take the wear and tear of pivoting. Not sure yet what I’d use. Another piece of steel, sacrificial piece of wood, search for a bearing...
The other option would be to build an oak “box” that acted as a chase and mount for your tv that went against the outside wall. Only a couple inches deep and slightly wider than the swivel mount. Cut holes in the counter where the cabinets meet the outside wall to chase wires through the new box. Secure cleats to the upper and lower cabinets, then secure the box to it. These need to be strong connections to carry the extended weight of the tv.
The box is this shape [ (top view) with the wide part being oak veneer and the short legs being 3/4” shaped to match the curvature in the wall and provide a vertical tv mount. Then mount your tv swivel stand to it.
There’s a couple options.