Backup camera and hiding the wiring..

I don't think you are going to find the space you are looking for in between the wall. I had a cabinet installed on the inside of where I was installing the camera. I ran the cables through the wall, into the cabinet, along the top rear edge of the cabinet, out the bottom of the cabinet, along the corner of the wall, through the bottom cabinet, then out the bottom of the trailer. I built and stained a trim piece to hide the cables down the corner. I went with a completely wired system, as I already had to run power through the wall, what was another cable and I already installed an aftermarket camera on my truck so the cabling was already to the rear of the truck.