This is an old question, but others might benefit from this.
Hate to say it but extreme aggravation calls for extreme solutions.
My brother and I have had this problem on cars and we COULD NOT find the electrical short. The only way we found one was using a bizarre method: We pulled the car into the garage at night, and had a good stash of spare fuses. After turning out the lights, we would keep putting the car into the situation which would cause the short to happen. In the dark, we would search for the sparks. Not the ideal solution, but it at least got us looking in the right direction. Once we narrowed it down to say, a two foot diameter area, then we would look for the problem in that area.
*****DO NOT use this method if there is ANY danger from gas (or any other flammable material, liquid, or vapor) in the area.