Don't have the problem your talking about, but while I was at the performance shop, the mechanic was looking at a car that had a drain on the battery when the car was parked just like yours...they were going over the whole electrical circuit to find the drain (at $45 a hour). Sounds like you have the same problem. I think there's a product on the market that allows you to disconnect the battery when not in use with a simple flick of a switch. It's mostly used for theft deterrant but it would stop any drain on the battery that you might have...course that won't solve your problem, just work around it.
CREWZIN