[Blue68]

jwitfield,
A question comes to mind. Are you intending to off road? If so, then under the bed would do two things to you, decrease ground clearance and add weight. If you put it under the bed you have to put in some armor as well to protect it from rocks and if you use the poly tank, from logs. In a roll over, if you leak in the cab, you were already smelling gas before the roll over or sloshing it out of the cap on corners and should have fixed it. A fuel cell in the bed is a good option if you can live with loss of bed space. I also like my gas to be out of the direct sunlight.

What ever you do, try to make sure it is DOT approved. This includes custom tanks. There are standards on welding and material (a stainless steel keg might make the standard, but who knows).