[CampNBrew2]

A couple ways that I've seen are secured underneath along the frame rails all the way to the back bumper and surface mount up to your mounting location. Or along frame rails, through the floor under/near the fridge, up the chase behind the fridge, through the fridge roof vent, surface mount to roof to the back of the trailer camera location.
Aside from somehow getting through your ceiling and back wall in the trailer with a grommet and waterproofing, there's just no way around seeing a few wires surface mounted.
Please do share your end result.