The trick is certainly having the 3/4-1 Inch board mounted to the wall first like Turkey 2371 is showing. The ones i have seen are usually maybe larger than what Turkey is showing but the idea is the same. This spreads out all of the weight over a large area. It would be neat to mount the board to existing interior wall stubs but not necessary. You can mount the board to 1/4-inch trailer walls using those expanding type metal wall mounts. Of course finding a wall stub is best.
You can paint the added board to meet your wall decor. The mounted TV will hide the board just fine when hung... Search google for "mounting LCD TV to RV walls" and when it loads up select "IMAGES" and google will show you many different ohotos of mounted HDTVs to trailer walls.
You shouldn't have any problems hanging what you wanting to hang if you spread out the weight over a larger area of the thin walls.
Use these type Expanding Hollow Wall Anchor Screw if you can't screw into a inside wall stud... These are also called MOLLY Screws...
photos from google images