If "safety reasons" is why you want to relocate the tank, consider that inside the cab might be the safer than under the bed. Inside the cab it's pretty well protected from just about any crash you might experience. Rollover crashes are an extremely small percentage of all car accidents something like 2%.
Don't forget that if you move your tank, you'll have a big hole in the side of the cab that you'll need to fill.
If you're currently smelling gasoline fumes inside the cab, you have a leak. Either the sending unit gasket isn't sealing or the rubber hoses on the filler neck are leaking.
I've owned two Fords and the current AD truck with gas tanks behind the seat and none of them smell(ed) like fuel inside the cab.
