A larger replacement tank is nice if you absolutely cannot lose the bed space. But for half the cost you can gain twice the capacity with an in-bed tank compared with a replacement tank. I have a 40 gal and it does not take up much of a footprint in my bed and it is under the rail and you can still use a bed cover if you wish. Mine is gravity fed with a manual shut off valve. I would like to add an electronic valve so I can leave the valve closed and not have to open the cover to switch it over.
I got mine for $80 on craigslist and has more than paid for itself topping off when you find those places that are 10-15 cents cheaper than your normal fueling places.
