Part of the problem is limiting options to LNG/CNG. Compressed natural gas has a very limited range. Liquified natural gas would do better, but since LNG tanks are cryogenic, forget about the trunk, it's full of fuel tank.
Propane liquifies by pressure alone, a Victoria could run all day on a tank that would leave luggage space, and can run dual-fuel, propane or gasoline. I know whereof I speak, over twenty years I have done after-market conversions on everything from pickups to floor buffers. If it runs on gasoline, I can make it run on propane. Computerized carburation has bumped the price to about $3,500 per, but one could refuel at the same places that fill grill bottles. Chemically, the difference is an extra carbon atom and emmissions are barely distinguishable. CNG has a better funded lobby.