This is a non-rule that should be a personal rule. Use a cell. Easiest way to prevent a catastrophic fire. Saves you, saves your car, saves your competitors. A gutted car that you escaped unharmed from is WAY more expensive than a fuel cell. Rubber bladder in a steel can only. Main thing to think about is how does a factory tank respond upside-down when it's hardest to get out of the car? I personally am skipping buying front struts and new tires this year to upgrade safety equipment.