A fuel cell is a good idea for any application that exposes a tank to damage. It is not a cure-all, it will leak if damaged enough. Be sure that it contains a bladder or foam and is not just a tank with a fancy inlet fitting. Bladders are more expensive but offer more protection. Foam slows leakage to reduce fire/explosion danger but does not positively contain the fuel like a bladder. Between the frame rails is the best location, which of course usually means behind the rear axle unless the tank is skinny. Lots of vehicles do it with one of those or the other.

Mac :{)

1962 K10 short step side, much modified for rally
1969 T50 fire truck, almost nos, needs a few things