I can't be sure from this if you don't need the internal lights on, but a tip I got from Gordon's book is that if you press the middle switch in the front interior light for 5 secs until it flashes that will stop the lights all coming on. Another press for 5 secs will bring them back to normal operation.
I'm in the same situation and have the same Traxide etc setup so I always do this when we're camping. I also put a strip led with a switch on my fridge cage setup that we can turn on and off as we need to see in the cargo area.
David

