They will want a metal box over the tank in place of a firewall for a hatchback or station wagon. It will need to be vented out of the car.I believe, someone correct me if I'm wrong, that if you ever end up at a track, they're going to want a firewall for an interior cell. Some of the rules seem excessive at times, but a fuel cell in a wagon doesn't sound too smart to me, with or without a firewall.