"We have received many emails as to why we don't offer a dual tank SVO conversion kit for a 123 300TD wagon. Installing an efficient and practical dual tank conversion in a wagon is challenging to say the least. The first big issue is the design and location of the factory fuel tank. It is located below the rear floor and is fairly narrow in height. To install a heated sump at the level of the tank outlet requires some very special component mounting brackets. The second issue is where to install the second tank. Putting a tank in the back of the wagon reduces hauling space and creates fuel smell and spill problems. Yes, even veggie can smell bad over time. Some have chosen to put a very small tank in the engine compartment for purging and startup, but you just end up having to fill it all the time."

http://mercedessource.com/node/3449