Yeah, sounds like a short to ground. High humidity and obviously water will leak the power somewhere eventually. I had my Optima red top in the Supra and it would run low after a few days of short trips to work and especially if left standing for a week. The alarm will drain it too, of course.
From being almost unable to crank the engine, it charged right up after a 10 mile drive and the charger said it was full within a few seconds of connecting it.
Perhaps these batteries are best for regular long journeys, despite the deep cycling claims?
I'd say that your alarm is the culprit. Have you got a microwave proximity sensor? My Sigma S30 has one and I reckon it must drain it a fair amount.