anyone have more than 2 fuel tanks?

[ed3196499]

My truck was plumbed for a third tank that must have sat in the bed, the fuel line and filter run up in the forward corner. I want to put a third tank back in but all the ones I see in catologs say not for gasoline. Are there any ideas of a how or where to mount another tank? I was thinking of finding one that sits in between the frame rails towards the rear since I dont run a spare tire under the bed I have the room.