If you have the chance, do yourself build an additional tank to measure, to be placed on the bottom of the floor, just behind the cockpit (Editor's note: the steel is the best material, make sure it contains foam or sponge antisciabordio or bulkhead. the unions of access would be better out of the cockpit as well as the traps to avoid stink (for diesel) or danger of explosive vapors (for gasoline). the best thing is to rely on a professional, the approval of these tanks is never guaranteed). A 200 liter tank is not higher than 30 cm, if it develops for the entire width of the platform, and also contributes to lowering the center of gravity of the car. The tanks truck, mostly cylindrical, are bulky and difficult to fix, and often those that are recovered from junkyards are full of rust.
If you really can not have a tank to measure then definitely opt for jerricans sheet 20 lt., Noisy but practical. There are military versions (Dutch army seems to me) special plastic read, not noisy, do not pierce with chafing and not rust, can also be used for water and do not form sludge, but as usual, they cost a fortune. Secure with strong belts inside the car in a position that makes possible their fill without removing them without having to download and half machine. Always remember to keep the center of gravity low and central. Five tanks of 20 liters will give you the peace of mind does not always stay dry. Warning: Before starting try them, and replace the cap seals because the shock of the track will test. Tip: if whenever the opportunity arises during the journey, filled tank and cans: in Africa do not always filling stations have tanks full and, if you are dry, it could happen to you than having to wait days for the fuel. If you're planning a trip just challenging dunes of leaving and returning to the base camp and planned to have to do more than 200 kilometers not fill Yourself 500 liters / kg of fuel.... would be implanted in only so many more.