Rearview camera hardwired on fifth wheel

I would look for ways to run it inside under cabinets, etc. If that doesn't work with your layout, I would run it right beside the support beam that runs front to back. Encase it in a piece of PEX tubing (water line) to keep it out of the rain, mud, snow, salt, etc. that you are likely to encounter. If it is within the tubing, it will be easier to zip-tie to other components that are underneath the trailer. I would have another connection at the front to tie in to the wiring from the truck.