Does the cabinet have a floor in it? If so, don't use a wall mount TV mount - use the TV stand that usually comes with them, and screw it down into the cabinet floor.
In my last fifth wheel I did this and it worked well; never had trouble with it and never had to unmount it for transit. In that one, the cabinet floor was at least 1/2" thick (particle board). I drilled three holes through the plastic/metal TV base and threaded three hex head machine screws through them then into the cabinet floor. I painted the heads black like the base and it looked fine.