I know this isn't addressing the cure, just the problem. If the shortened battery life has anything to do with your driving conditions (rough roads leading to premature shortage in the plates) you may try one of the spiral-wound type batteries, i.e. Optima and Exide. There are plate separators between them to prevent the vibration woes. You may also consider one of the dual purpose, cranking/deep cycle batteries, that Optima sells. The deep-cycle aspect should help offset the higher-than-normal parasitic draw you have.

Just a thought-
Randy