I've got a 2003 4.2 turbo diesel Troop Carrier, with dual 90L tanks. I get on average 600K per tank mixed driving conditions and loads, before the light comes on. Then filling up is around 140L - 150L, for both tanks. Using the FuelLog app, I average around 12 to 12.5 L/100Klm not towing. So if you use say 13L/100Klm, to allow for whatever, Orange to Melbourne is around 800Klm, 13L * 8 = 104L - so you should do it easy.