Steve,
What you say almost exactly matches what happened to our RV's original OEM-installed two Group 24 batteries and how we use our 12 volt power when we drycamp.
Our two OEM Group 24 batteries failed in about 10 months (November of 2006) after we bought the RV in January of 2006.. The RV dealer replaced them at full retail price with two Group 29 AGM 12 volt batteries at about a $47 upcharge difference per battery that I had to provide. Those two AGM batteries are still in our RV and seem to be performing well enough for our drycamping style.
When camping we keep them charged in three different ways: Using the Onan built-in generator to power the stock converter, using a little Honda 650 watt portable generator to power the stock converter, and (rarely) idling the main V10 engine for 30-45 minutes to begin the charging and then continuing with the Onan or Honda - depending upon how quiet we want to recharge or how much other power we want to use during recharging. This system has served us well for the 8 years since the warranty replacement batteries were installed.
