That is why I wrote my guide, I tell you ahead of time what to do and what to watch out for. MOST of the time, finding excessive battery drain is not all that hard.
In most cases, I have it isolated in under 30 minutes.

There have been two cars that proved very difficult, one was a car that had a leaking pass transistor in the Climate Module - it was holding the duovalve closed (which requires over an amp of current) even with the key off.

Spec is "Less than 55ma (.055 amp)
Base/SE models will run .020 or so and limited/SRTs .040 to .055 or so; that is, when all is right with the car.

In any event, once you find the fuse that the extra current is passing thru, you can use the diagrams in the wiring chapter to find the item that is at fault.