Parasitic losses can drain the batteries down...
You could try putting a battery disconnect switch on the ground terminals, and completely "cut them free" of the coach.
I put one of these in my Outlaw, and it did a really good job. I would only hook up to shore power for about one day a Month, and the batteries stayed up. Prior to it's installation: they'd be discharged in about four days.
http://www.thorforums.com/forums/att...1&d=1560724115