I'll stand by my diagnosis of the aftermarket cd player. Alberta gets more than a little colder and for a lot longer than Tennessee, and that takes its toll on car batteries.
We pulled all the fuses and the alternator wires, and saw no change in current. This left the cd player, or a short that was after a 44 ohm ( 12 / 44 = 270 mA resistance and before any of the fuses we pulled.
Depending on the size of battery you have and the type of GPS, detector and alarm system, your claim of 3 weeks sounds reasonable to me as long as it wasn't -20 C.
I know with my deck, there is a wire that is supposed to be connected to the always on circuit, but there is also a wire that is connected to the ignition switched circuit as well.
When we reconnected the ground to the battery with the key off, we could hear the motor in the deck start up and then stop. So the deck was doing more than just keeping memory set. The other circuits that sense and load a cd were powered, and probably the 270mA current sink.
I could be wrong, but I'd bet a beer I'm right...
And being a Scot, I hate losing...