Paul, okay then two options you have are:
1. Add a 12 vdc fuse panel where your
battery wires come inside the camper. You could have 3 circuits (one each for
lights, vent fan and fridge). Note that its generally not practical to power the
fridge with the battery because the
fridge will exhaust the battery power in a few hours. Use a smart charger to charge the battery when shore power is available, and/or add a
solar panel and
solar charge controller. I went this route. I also added a small AC to DC power supply for providing 12vdc power when shore power is available.
2. Add an AC/DC power distribution center combined with a AC to DC power converter and battery charger. This is a one stop solution. Again you can also add a
solar panel and
solar charge controller.