Running out of fuel is not the only reason you might need an auxiliary fuel tank.
When you think about why you might need an auxiliary fuel tank, it's not just the prospect of running out of fuel you need to think about. For example, the remote tiny towns through which you plan to travel might have extraordinarily expensive fuel, or the service station might not be open.
And if you're considering purchasing a long fuel range tank, think about this...
Running out of fuel is one of the risks when you're on a long off road trip, but that's not going to help you if you're on a tough trail and you sustain some damage or get a leak in the tank. So if you're prone to head for some particularly gnarly tracks, put an auxiliary fuel tank on your shopping list.
Being able to switch to an auxiliary fuel tank gives you incredible peace of mind if you're driving deep into challenging terrain. Even if there's no fuel in the auxiliary fuel tank, you can still salvage the fuel left in the primary tank, transfer it and get on your way.