Welcome to the world of Gemini's! My previous boat was a 2007 105MC, Hull 987.
Your Westerbeake alternator should be putting out 14.1v, it's a standard 55 amp alternator, which means at idle it's only really dumping 20amps. You need to get it checked.
Gemini's don't come with chargers, but I'll assume the previous owner put at least a 20amp onboard. If he did, and it's working you should plug your Honda directly to the 30 amp plug and use it to power your charger, that is the most efficient way to use your Honda as the 12v outlet only puts out 8 amps.
If you have not done so yet join the Gemini Cat's group at yahoo, great information.
If you have davits you should look at hanging at least a 125w panel between them, it's not hard to do and the benefits are outstanding. You can also put it on the dog house roof (simpler install) - then pull the boom to the side with the traveler so it gets good sun. A solar panel is the only way you are going to be able to keep those AGM's topped off and AGM's need to be charged to 100% periodically or the die a premature death.
Your batteries should be on two shelves, the upper shelf is likely the group 24 starting battery and the 8d's on the bottom (that's a lot of weight on the port side by the way).