My first truck was a '67 C-10 - tank behind the seat, then I owned and drove a '73, '74, '76, '77, '84, '87, all GM's - all with tank/tanks outside the frame rail/s. The 1974 had a little mishap in 1975 on the Divide in Colorado, truck rolled countless times down the face of Red Cone mountain and came to rest on it's wheels, no gasoline issues and no fatalities. There have been and still are millions of trucks with exposed tanks on the outside of the frame, many are right under the driver's door and used as the step. That's my story and I'm stickin' to it.