Best info I've ever seen on adding a 3rd AC... (
http://www.irv2.com/forums/f115/addi...ner-46004.html). Very well worth the effort!
We have an Endeavor PAQ with Atrium windows and the big one-piece front windshield, and it makes a
HUGE difference with the extra AC. You can go from hanging meat inside to just plain keeping it cool when facing the sun. I also wired the extra AC to be able to run off of either the combined 50amp line with the other 2 units, or run off a dedicated 30amp line just for that middle AC. No real problems with running everything off the 8kw Onan genset either.
As far as snaking the wires, I went from the AC itself then thru the ceiling material over to the spice cabinet next to the sink, then back behind the monitor panel. From there, I went down and under the floor and back to the electrical panel. Obviously, your floorplan may dictate something different.
Hope this helps!