Originally Posted by wstar

Even if you mount low, you don't want to intentionally put weight at the far rear end of the car. Yes, your weight distribution number for F/R would get fixed, but keep in mind that's just an approximate metric; the real goal is a well-balanced car, and a well-balanced car keeps as much weight as possible close to the CG. Hanging weight out at the end is making the car into a pendulum; it will tend to over-react.

What clint says is the truth: the stock location is pretty ideal all things considered. It's hard to place a fuel cell's weight better than that, especially given it saddles over the driveline hump to get even lower. (And really, I can't imagine a safe and correct switch to a fuel cell that would cost less than phunk's kit at the end of the day anyways by the time you factor in all the parts involved, especially if you want to fill from outside the car).

Also, while good fuel cells are designed to minimize fire risk when impacted, it's still not a great idea to stick them out on the edge of the car where they're most likely to be impacted in the first place. If I had a fuel cell, I'd at least want it to be inside the volume of the cage.