It's interesting drivel. The water heater would probably be best replaced with a comparable LP only unit. If it is LP only, you don't have to worry about hooking the electric to it.
For the brake controller, when you push the slide lever over, do the brakes on the trailer apply? The breakaway switch should be wired in to the main brake wire, one wire to the brake wire, and the other wire to the 12v
Also, there are more of us than you would think here interested in things like railways (railroads), aircraft, and ships, as well as the aluminum trailers.