Quite awhile back I was at a Army surplus store and found the actual locking mounts for ammo cans. They were pretty sweet. If I were you I would look for one of those. They hold the ammo can down very securely, and have a release so you can take it out when needed.
If that isn't an option, then I would just bolt it out of the way in the back cargo area. Make sure to silicone the holes, that way if you get an exhust leak(say, right side manifold crack) it will not come into the cabin.
Casper
:smiley_drive: