Whenever I got to start up when the outside temperature is near or below zero, a strong (gas station) fuel odour flows directly into the interior (especialy when heater fan is running). I have noticed when this does happen after driving a short distance, there is some pooling of fuel under car (caution: do not drive car when there is fuel leak...I have been lucky and will not drive until fixed). However, I was out underneath searching for the leak today (weather was 3-4 degree's C') and could not even smell any such fumes or see any type of fuel leak. It is puzzling to have the fuel leak be so selective during certain outside temps. I could be wrong! Any ideas would be greatly appreciated....

It sounds like a loose coupler fitting. The extra cold would make it contract to loosen it even more.You might want to check all of the fittings where you have a flex line coupled to a ridged line.If it's leaking as bad as it sounds, there should be "clean" spot aroundit.