Wouldn't it be better to use 2 tanks? If you have a fuel problem or run out of fuel, both engines are going to shut down with one tank. At least you would still have one running, so you could make it back to the field and land if you had two tanks.
Boomstriker said to mount the rear tank 'back wards"...no, it should be mounted just like the front tank, facing forward, with the lines going back over the tank to the engine. Just for my planes safety, I would use 2 tanks myself.
Suptter