I don't know what the rules in Oz are but the USCG has some very specific ventilation requirements for storing Gasoline (petrol) below decks. In
Florida they can confiscate your
boat if your compartment does not meet the ventilation requirements. There are no such rules for diesel
tanks so it is unlikely that your diesel
storage compartment is adequately ventilated. You might want to consider a
bilge blower and additional ventilation. I know a guy that blew up his
boat when he sprung a small leak in the filler hose of his below
deck petrol tank and didn't blow his bilges. Fortunately he was not seriously injured. It can be done, but please make sure you are able to deal with Petrol fumes in your bilges without killing yourself.