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.