Mercedes Sprinter: Upgra-inch wheelbase) or Double It to 56.4 Gallons (170-inch wheelbase)

The only elegant solution to having more fuel is a larger fuel tank. Not a dual fuel tank with a pump system or external fuel cans, but a larger fuel tank that works exactly like the stock fuel tank.

Mercedes Sprinter: Installing a Higher Capacity Fuel Tank (ACGB Tanks)

ACGB High-Capacity Fuel Tanks for Mercedes Sprinter