Little update. I haven't installed in a rail car just yet, but I mounted the system to my rock crawler and drove around the outside of the house while I sat inside, looking at a 32" tv I have in hobby room. Worked better than I expected. I had some static as expected, but overall, a good picture. Now to get a longer HDMI cable so I can put the Rx outside and see the results.
Going to try and mount on front guardrail of engine. Like to put inside of the body, but gets a bit toasty and needs some air movement to help keep cool. I hope it will get enough just from the train movement at smph 20, and house temp of 73-75. If not, have to add a small fan for additional air movement. At that point, for the looks, might be better putting the system into a boxcar and having engine push it, or mount camera on top of car overlooking engine.
Setup with battery power 1st. If all goes well, maybe pick Stan or GunRunner's brain on a little capacitor bank so I can borrow little juice from rails and keep system online full time. Only other thing im hunting for is a electrical switch I can change between cameras. There is some stuff out there, but I would have to use my car or plane Tx / Rx to switch the pwm signal board to view another camera or 2.
But first, build the railcar with one camera on battery power, then will move on to the next step.