I took some photos when I removed the outside panels.
There is a plastic piece behind the aluminum skin that provides
support. The thick black wire goes to the camera.
The wires run between the fiberglass insulation and the skin.
The wires run all over the place. The run through holes in
the supporting ribs that form the roof support.
I don't think that you can snake any wires through the roof.
I added some new wires for a camera but I had it all apart.
There are a number of conductors in the existing camera cable.
You probably can run your new camera using the original cable.