You will probably have to mount a back board up first maybe using MOLLY BOLTS. The trailer walls are too thin to support any weight from one screw in the wall. The screw will pull out. The idea is to mount a large 1/2-inch thick board across the area to spread out the weight and then you can use regular wood screws to hold up your HDTV mounts to the backboard.
Couple of ideas shown here
This is a MOLLY BOLT. It spreads out when you install it to spread out the weight around the bolt.
You can find a very large selection of different HDTV mounting hardware at WALMART in the TV section. Also on AMAZON...