Everything runs in the ceiling. It is a very difficult area to work in because getting the skin down is impossible without help, and even then it's not pretty. I suggest cutting the skin into manageable segments. This is not beautiful, but it doesn't have to be ugly. And it doesn't significantly affect the longitudinal strength of the skin. The interior skin adds little to the strength of the shell.
In this 23' 1973 Safari I had already cut the ceiling skin at the center vent when I removed and sheeted that vent closed. Now I wanted to remove the 300-ohm TV twin lead and replace it with RG-6 coax. Turns out that with the skin removed, the existing twin-lead could be used to pull the coax for a total replacement. Now I have coax from the bedside up to the control center in the front dome.
First, you remove the A/C cover and the interior hard mount.Then pull the skin down.
Then cut the skin approximately in the middle of the A/C. The strips on the sides are narrow there. Once cut, reinsert the piece that's still attached.
Sometimes you can find a rib that can provide a convenient place to reattach the two pieces of skin. If not, rivet a tab on the ends of one and then attach the other. You can even make notes that will be hidden under the A/C cover.
Put the A/C cover back in place and the new cut is hardly visible.
By the way, this is the Burning Man trailer, so it doesn't have to be pretty, just functional. On the other hand, I have done this to several other trailers where it had to be pretty and I found that that was fully achievable.