Auxiliary fuel tank

I'm looking to fit either a 45-litre or 100-litre fuel tank to my LR 110 County Station wagon. Depending on which of these it was, that would give extra range of approximately either 495 or 1100 km (at a fuel consumption rate of 11.3km/litre, present consumption). I live in Oman, but am not really buying the tank for use here (diesel fuel is probably available, I've found, often enough to avoid running dangerously low). The extra tank will be for future travel after Oman, perhaps in out-of-the-way places. But how often and where might one need a range of 1250 km (which the smaller extra tank would give), or 1850 km. or more, which an extra 100-l tank would provide? That seems like an awfully long way. (An area must be pretty remote if there's no (diesel) fuel for more than a thousand km. Or is there also the matter of being able to buy clean fuel?) Anyway, would it be good to get a 100-l tank, I wonder, or just a smaller one? Please advise.

the advantage of the bigger one is that you could fill up with more 'clean fuel' and be running on that for longer, also mean you dont need to worry about filling up as much....but each will be more