I see you're trying to mount the tv to the outside mount and there is limited space between the wall of the trailer and the backside of the tv. I might think about adding some spacers between the tv and the mount so that you can get the clearance you need. I say the tv and not the wall of the trailer so you won't have to worry about compromising the seal. Try you local hardware for some 1/2 inch spacers and don't forget you'll probably need some longer screws too. Good luck.
Looks like you could put some washers or spacers between the TV mount and the TV. Make sure the screws don't go through the led panel though. I intend to get this same mount for the bedroom wall and the outdoor wall. One less TV to carry. My TV connections are on the side of the unit fortunately.