In Alaska, the temperature reaches MINUS 20 degrees frequently. But still, gasoline stays liquid even at minus 50. It doesn't matter what kind of vessel you use to store or carry the gas. The freezing point does not change.
Keep water out of the gas by keeping your fuel cell filled as much as possible. This will prevent water vapor from condensing inside the tank.
Gas line freeze is not caused by frozen gasoline, it is caused by frozen water that has accumulated in the fuel tank and fuel lines.