Yeah, back in the 70's, I added a second, factory tank with manual switches to at least 1 Chevy and 1 Ford truck. I was pretty proud of my second addition when I figured out how to switch the sender from both tanks to the single dash gas gauge (high school student at the time).
My dad, as part of his construction company, had custom built line box beds that would transfer from old truck to new truck for the fleet of F-350s that included 2 separate tanks, one for gas and one for diesel. They weren't plumbed into the fuel system, however, and refueling required one to stop and pump from the bed tank to the truck tank.