Yes you are correct there is a drain occurring somewhere.
There is no way to track this down with a guess, you really need to get hold of a mulitmeter with current or amperage capability. They are not expensive but getting hold of one in the alps might be tricky..
Either way, with the engine off, you need to remove a battery terminal, set the Amp range to 0-10 amps or what ever the nearest setting is, then put this in series with the battery terminal and the cable. This will measure the current coming from the battery with the ignition off.
There should be some current for the radio memory etc but it should be no more than a couple of milliamp.
It will probably show a few amps if there is something remaining live. The process is then removing the fuses/relays in the fuse box one at a time to track down the circuit which is staying on... Once you find it, you can remove the fuse whilst the car is switched off to prevent the drain... be sure to replace it when driving though if its an important circuit...
I hope this helps... if you need any further information just get back to me...
All the best