FWIW, a small 35 gallon auxiliary tank probably takes as much space as 4 or 5, 5 gallon gas cans. Not as easily removable, but there are always tradeoffs. How much stuff do you actually haul in your bed usually? Probably not too much or you'd have gotten the full size bed.
I paid less than $400 for my 35 gallon tank and pump. It's less than a foot deep, and it sits even with the bed rails. Works a treat for me. And I got it for a more stress free travel. I no longer worry about getting into and out of gas stations with the trailer in tow. I stop when I want to, not when the truck's fuel tank dictates it. Much nicer to take a break in a rest stop, or city park rather than a noisy, dirty, crowded truck stop/fuel station.
