Long term storage of Bushtracker

G'day Greg, can I ask why you are storing it in an Industrial shed ?
It is a Bushtracker and is made to stay outside in the elements, that way it takes care of itself as far as the electrics are concerned. The solar input is enough to keep the batteries in good condition until you get back. All you really need to do is empty the water tanks, and block up the shower and sink drain outlet hoses to stop the bugs getting in, and the hornets from building their little structures inside the hoses. Then put a litre of kerosine in the Webasto fuel tank to stop the algae from growing in the diesel, empty the fridge and open the door,and your all done.

However if you must store it in a shed, plug it in to the mains 240 volt power supply and turn on the battery charger. Or better still put the charger on a time switch to come on once a week. Empty the fridge and open the door. Empty the water tanks. I notice you have water filtration, so I would remove the cartridge and replace it when you next want to use it.
Hope this helps, kind regards, Keith & Joan