If one of your trailer's bathroom walls is a inside wall, that is running front to back and can be accessed from the other side. A guy could place a Grab bar just out side of the shower's wall running up and down hand high. This bar could be bolted onto or threw a (say 3/8" thick) block of polycarbonate (Lexan--tough and water proof, threw the wall and into a finished Oak block, the same size or larger, on the other side. Think sandwiched between in order to spreading out the load. I would not go threw where the shower wall is, you'd be asking for trouble. Most Rv showers are not that big anyways, a bar would be sticking out to much and hinder movement.