A number of folks have complained about the size of the Sprinter fuel tank. Mine, and for quite a few years after, are 100 Litre/26 gallon. When MB designed the 4 wheel drive system for the sprinter, they had to reduce the size of the fuel tank to about 24 gallons and they made this change universal rather than making two different fuel tanks. In a Sprinter van, its not an issue given the 24 mpg or so that they get, but in the motorhomes, with 16-17 mpg, it becomes an issue, especially out west where the fuel stations can be far apart.
Charles