attached is a photo of a 55 L tank,
the tank is used in europe on thousands of cars.
the tank fit perfectly with no modifications to the spare tire hole. and is held down with the spare tire screw.
the tank is sealed around the bottom and there is a upper cover. the connections go directly out of the car cabin so if there is a leak in the valve , hose , fittings the pressure can easily go out side.
Now that's thinking out of the boxer
fyi all 05 + legacy's have built in code reader