Having checked the wiring this drawing is as near as possible to the Wanderer's actual wiring.
You can see from the drawing that the "Caravan" area is electrically isolated while the vehicle is in motion, except for the fridge, via the relays.
Recently, Sept 2011, the fuse 25Amps located inside the engine compartment. See location on the drawing as: ' Veh. Battery +Ve' had melted, but the fuse was intact. I attributed this to the fuse holder being black with mold. This in turn caused a resistance and low charging current to the leisure battery. Where there is a resistance there is heat. This in turn melted the fuse retainer.