First post -- Electrical gremlin

Greetings everyone!
My 1992 trooper has a strange behavior. It seems that there is a current drain somewhere that can't be found by the local electric shop. It shows up whenever there is a lengthy (but small) load on the battery. I'll explain:
The first time I noticed this (shortly after purchasing the trooper) was when I was washing the truck and I kept the doors open, but otherwise everything off. The alternator started smoking. Since I had been washing and prettying the engine, I blamed the Armor-All, thinking it got in and shorted it out. Off to the shop the car went to rebuild the alternator. After a few days, again after having the doors open for a long time (this time installing audio components) the battery went dead. Back to the shop where they replaced the diodes in the alternator (under warranty).
After a month or so, I again had the doors open for a couple of hours and (yes) the battery was dead again. The shop this time changed the battery. So now I have a rebuilt alternator and a brand new battery.
This past weekend, we had the air conditioning condenser (missing when I bought it due to a front collision) and the AC shop (yes, again) had the doors open and the battery is now dead. I will take the trooper tomorrow to be checked at both shops, but I thought maybe someone had a similar experience and wouldn't mind sharing some advice. Thanks in advance