See post #40 to see what to expect behind the wall panels.
You'll have to remove the inside aluminum framework around the door; window frames, and interior panels to gain access to the hinge bolts behind.
As Martin said, the hinges are labelled for trailers, so U for Upper hinge is to be mounted on the bottom, and B for bottom on top for these to work correctly.
Like my post stated, making a 1/4" aluminum plate, drilled, tapped and vulkemed into place on the inside of the wall to secure the hinge screw bolts means you could remove hinges without having to remove inside walls in the future. Plus makes the mounting of the hinges that much more secure.