I'm sure someone suggested this before on another thread to disconnecting the earth cable from the battery & putting an Ammeter in line with the battery terminal & Battery earth cable. Make sure the ammeter is set to measure amps & see what it registers. Then trying pulling out the various fuses until you find the one that looks like its drawing the current. It might help track down the problem. Never tried this but it might be worth a go.

Just make sure you don't turn the engine over.

My battery was going flat over a 1 week peroid & it was down to the boot light.