<VV> Non-Corvair Specific: Gas freezing?

[ricebugg at comcast.net]

All:  My wife ask if we should fill up the tank on her RAV tonight.  We then had a conversation about keeping at least half a tank of gas in the car during cold weather like we are having now in Central Illinois.  She thought it was to keep the gas from freezing.  I told her it was to give you heat if you get in trouble, assuming the motor is still running.  I realize condensation inside the tank can freeze in a fuel line, but that it is rare.  Never had it happen in 40 plus years of driving up here. 
 
I assume one of you chemist types will know the answer here.  The question is, just out of curiousity, what is the freezing temp of gasoline?  I assume it will freeze at some temp, but so far down the scale everything else in the car has become non-functioning. 
 
Thanks,
 
Historically Yours,
                    James Rice