diagnosing a mystery current drain

[davidpertuz at mindspring.com]

My G20 has been suffering from dead batteries recently, and while the initial investigation pointed to a bad battery, it now seems to be pointing to some unknown current draw when the car is off. The battery will go down to 3.x volts in about a day when in the car, but seems to be normal (so far - it's only been overnight) when out of the car. 

Can some of you who are more electrical people than I am (I'm an engineer, but while I am a lot better at electrical diagnosis than I used to be, I'm much more of a mechanically-minded person) lay out for me the most time-effective method for finding what'd draining my battery? 

Can I do something like hook up my multimeter probes across the fuse terminals for each fused circuit and look for current there? Any better ideas? Thinking of all the things that could draw current can be overwhelming and suck up a lot of time. Rapidly eliminating things that can't cause it or aren't would be much faster.

Suggestions welcome. We are driving to Michigan this Friday and I'd like to take my car. Mostly my car sits in the garage and gets driven once every couple of weeks or so, and I'd like to give it some exercise.

thanks,
David