Gas Storage
While I no longer own a boat with a portable gas tank, my sense of how to store the tank is this: keep the tank in a separate, vented, compartment. Most portable tanks, i.e., for outboards, are not too leak proof and most need to be vented in order to work. Keeping such a tank inside the boat creates the possibility of volatile fumes getting into places inside your boat that are not properly vented and could be very dangerous. I'm not sure what year Hunter 25 you have, but if I recall correctly, many of the older ones had a very nice fuel storage compartment in a aft lazarette. Keep the gas there.