Adding a second tank

I'm reallly thinking about putting the gas tank from the donor truck in as a 2nd tank in my truck. I have two places in mind. The first being in the bed up against the forward most wall. It would be the easiest place no doubt...but I'm not sure if I want it there. The other place would be under the bed somewhere.
Opinions, ideas, (and pictures if you've done this) would be appreciated.
Thanks



