I have not mounted anything to the outside walls other than with 3m velcro or short 3/4" self tapping screws (safe since I know the aluminum framing is 1" thick). I used a stud finder to tap into the framing when using the screws.
Most TV's I've seen mounted have been to an interior wall specifically designed as a TV Mounting place. Usually have a sticker desiginating it as such if a TV was not included with the trailer when bought new. This is because as a general rule, I don't think most of the walls are built to support TV's on a mounting arm without this additional beefing up of the mounting spot.
My suggestion to you is to look for an interior wall that would work for you and either remove the paneling and beef up the horizontal supports to allow something significant as far as mounting screws OR mount a peice of finished plywood or 1"x10" between 2 vertical studs with multiple screws into each vertical stud and then mount the TV bracket to the board.