There is no one who currently makes a larger fuel tank for my truck but burning diesel I would love to have one. It is not a matter of saving money on diesel but in having a lot more route flexibility when I don't have to worry about where I can find a station that pumps diesel. With a gas engine I would not care about the extra range of a bigger tank.
When it is windy and either towing or hauling a full load my truck gets 10 MPG and so I have a range of about 300 miles and that is not a lot in the rural areas of the west.