I'm using the light color scheme and if I could read your post, I'd take a crack at answering it, lol.
Seriously though, I just "selected" it by dragging the mouse and it shows up. Consider letting the system use default colors for your main text because those of us who are visually impaired may use the other "light" color scheme and your green doesn't show up well.
I think the big issue is where to put it. On mini-trucks there just isn't a lot of room under there. Possibilities are to mount a fuel cell where the spare tire is, in the bed, etc. There's no place to put another whole factory-style fuel tank though.
Since we have a high pressure injection system, you would probably need fuel pumps in both tanks, switching of power and valving, etc. Alternatively you could just use a "transfer pump" to bring fuel over from the secondary tank when you needed it and dump it in the main tank.
You'd need to plumb it carefully to keep from having emissions issues if the system can't hold vapor pressure.