Re: Auxiliary fuel tank
Our 89 Ford SMB has dual fuel tanks. One is in the center of the driver side and the other is centered behind the rear axel. There is a toggle switch at the bottom of the dash to the left of the steering wheel that is used to switch from the front to rear tank. When the switch position is changed the fuel guage shows the amount in the newly selected tank. I believe there is a pump in each tank. There is also what I will call a transfer control unit mounted on the frame. If I remember correctly the tank pumps into this unit and then to the engine.
You may be able to find all the necessary pieces in a junk yard. I know that the transfer control units are still available because we had to replace ours because it would only work with one tank.
Our two tanks hold about 35 gallons between the two of them.
Edit: there is a separate filler port for each tank, one on each side of the rear wheel.
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Current van: 2002 Ford E350 extended body camper with Colorado Camper Van pop top and Agile Offroad 4WD conversion.