Sure, but I only used the roof box on occasional long trips when we had lots of luggage (e.g., visiting the grandparents interstate for Christmas). So I might h

Sure, but I only used the roof box on occasional long trips when we had lots of luggage (e.g., visiting the grandparents interstate for Christmas). So I might have paid a few tens of dollars extra in fuel, but it was certainly far cheaper than buying a bigger car when we otherwise didn't need the extra space. The roof rack and Thule box cost maybe $1200 AUD. But the rack was also useful for attaching bicycle carriers.