I found my culprit. Wasn't my extension cord from the house, but, the cord supplied with
the car. I discovered humidity entered the cord from the small holes in the plug itself on
the car side.
I checked for resistance and only found some on the Ford cord. Left it in the house for about
a week, and checked it again, and this time, it was good. Began using it again, only to trip my
breaker again about a week later after having had some snow fall. Removed cord, and checked
again, resistance appeared again on my meter.
Put it near the wood stove for a few days, and then began to examine the cord, when I noticed water
residue around those two tiny holes. Filled them with dielectric grease, and have been problem free for
many weeks now.
Just thought I'd post this if anyone else has ever had this problem, or, someone in the future faces this
situation. I know not too many people use the block heater, except for a few of us Northern folk.
Below is a pic of the cord with the holes I speak of.