I have a couple of these deep cycle 12V Group 31 AGM batteries in parallel under the step (the stock location as provided by Winnebago) in our Itasca 24V Class C. They're 115 amp hours each, so they provide a total of 230 amp hours. Their specified float voltage is 13.6 volts, so stock single voltage converters don't dry them out over time. Also since they're AGM, they charge faster with any voltages in the charging range than wet cell batteries do. This means that they can both be floated and charged fairly quickly using just a stock 13.6 volt RV converter. That's what we do with our RV:
http://www.fullriverbattery.com/product/batteries/DC115-12