Original underseat tanks are available from Jim Carter Truck Parts. I added a another tank behind the seat. I just made a cardboard template to see what fit. I got some sheet steel cutoffs cheap from the local metal company -$27.00 bucks. So no I have 18 gallons under the seat and 13 behind the seat. Range- around 450 miles. I bought a new sender that works with the original 6 volts and a fuel selector switch. It also shuts the fuel completely off. The filler was the only odd part. It ended up on the rear of the cab, but it works fine for me.