I definitely agree with Karl. Carry as much fire extinguisher as you can justify fitting in your rig. Even the larger ones will not last long on a gasoline fire, the small ones are about like pissing into the wind. Remember Crash's story about the dude who rolled his rig without a proper battery tie-down... poof, break out the hot dogs cause it's time for a weeny roast.
I did a very stupid thing one time, but it was an experiment that I learned something from. Dumping out the contents of an old gas tank and lighting it on fire in the driveway is a BAD idea, even in the rain. The big extinguisher I had was not effective at putting it out because of the volume of gas on the ground... I can only imagine if it had been a full tank with constant leakage and a rig sitting there upside down. I had to run around like a chicken with my head cut off for a second looking for a hose, but the gas did finally burn up without lighting anything else on fire. If anybody ever doubts the extreme flammability of gasoline, just ask me and I can re-iterate it for you. :redneck: