Remove a battery terminal with everything shut off. Put in a milliammeter and measure the current. I don't know what's acceptable for your particular car, but if you're over about 100mA, go looking for why.
Also, are you sure on the alternator? It's at about 14V when running?
Battery connections. Be sure at the battery and wherever it's connecting, but that's basic stuff.
Subarus are fairly normal. It's not like it's a Lotus, where killing a battery in 2 weeks is normal and expected.