I have learned something today. The power still only comes on when the ignition is at ACC or on. Did some circuit hunting and found that the rear power outlet is serviced by a relay that is located above the rear wheel well. FFS why must everything be so hard. The drawer on that side will have to come out to get the trim off.
The Bushman fridge I have has a low voltage cut out at 10.4V. Time will tell but I'm really not too worried about a slight voltage drop. If it proves to be an issue I'll cross that bridge when I get to it. Plus by the time I take the relay out of the circuit the drop will probably improve.

