For me what would make sense would be the in bed tank and a pump.For one if you have a diesel generator you can fill it via the pump.meaning an external pump like some guys have to refill heavy equipment.You could also tap in to the regular fuel tanks as well so you don't have to get out and fill your own truck.

Some of the tanks I have seen take up about as much space as a tuck toolbox that goes across the back wall of the bed by the rear window.