This probably doesn't make sense, but I had a very similar issue with our SC. I'd replaced the alternator and the battery and it'd still die after just a few days of non-use. While idling, I was getting about 14.4 on the battery which made this even more baffling. Also a couple times while driving, the car would just have a total electric failure, but the battery drain had gone on for about 5 years.
I then did part of the "3 step ground process":
-Connected the neg post of the battery to chassis - near the left suspension pillar after dremeling the paint off to get good contact.
-made an engine to frame connection. Used one of the bolts on the intake plenum to another pillar bolt , again took some paint off to it'd connect to bare metal.
-while under the car for something else, I discovered where the stock engine-frame wire was (see my post). It's on the left side of the transmission just to the right of the cat and connects to the frame on the left side of the cat.
Look for my post on this subject - I posted a pic of where the stock wire is. It's pretty much right under the driver's seat from what I remember. I took these connections off and cleaned them really well.
-I didn't do the + to the + post of the alternator. I just didn't think that was worth it.
Since I did these, the 'draining' issue disappeared and it hasn't died. I'd say first get a cheap multimeter, but the easiest, cheapest thing you could do is probably clean the stock ground connection.
I found the link with the pics. Good luck and let us know how it goes..