I wouldn't carry a gas container around inside of my car for anything other than going to the store to refill it, and even then.. I don't like the idea.

If your involved in a roll over accident or anything that causes that can to leak and your setting yourself up for immolation IMHO. That's pretty much in list of top five ways I don't want to check out of life, if you know what I mean.

Also, getting that gas smell out of your car is almost impossible...