Jason, referring to Gerald's comments, if it is at all feasible the best thing for your coach would be to go with four 6v deep cycles for your house batteries. They have more overall amp-hour capacity than 12 volt ones. But you have to have room for 4 and will need the rewiring for a combination of series and parallel. That should be done by someone familiar with your coach.
My batteries are 12 years old also and mostly shot... my solar and inverter chargers don't know what to make of it, the solar is constantly bulk charging (boiling off water) because the voltage never gets over 12... good bats and charge systems should stabilize and float at 13.3-13.5v. 12 years is extremely unusual and most people are lucky to get to 8 years, if that. As Jerry alludes to, your main issue is aged-out house batteries. Like Steve recommended, deal with that first before worrying about charging possibilities.
That said, and you can find someone with the expertise to rewire and install them, if you are willing to toad trip inland to Eugene or up to Astoria with your old batteries in hand for core exchange value, one of the better 6v Interstate golf cart battery deals is at Costco. As Gerald noted, you'll have a time getting 12v deep cycles anywhere, wet cell or not.
Joel
