Anyone build their own fuel cell?

[Tdubbyount]

So I'm thinkin about building myself a new gas tank. I got tired of screwing with my disfunctional dual tanks and one 16 gallon tank just didn't cut it for my particular driving style. So I pulled the tanks and filled up the space with my new 3" mandrel bent exhaust

Anyway, my plan is to build a cell that sits in the back under my toolbox. A "slip tank" as we call it on the farm. I thought about just buying one until I looked at the prices. And none of them would fit how I would like it anyway. So I'm looking for some pointers. What gauge metal? It's gonna be steel not aluminum. Most joints will be bends not welds. It's most likely gonna be Mig welded. I plan on having my filler inside the toolbox, with a vent outside somewhere. I want it to be somewhat discreet, since it's not exactly DOT approved. I think I'll be able to fab in a sender body off of a blazer or k10 tank I have. So what do you guys think? Anyone done this already?

Oh yeah, and I gotta show off the new exhaust I built...(: