Also, you may want to get a Tri-Metric 2025-RV battery monitor (Bogart Engineering) to really check on those 6V batteries. You can get it for about $200 with the wiring kit and 500A shunt. Search the forum for Tri-Metric and you will learn quite a bit about maintaining your battery's state of charge, etc.
Another great option for boondocking is to add some solar panels to put Amp-hours back into your batteries as you draw them out. There are quite a few threads on the forum that provide the ins and outs of solar. It will cost you some $$, but may be a better option than running a generator.
Finally, for a really good (but wordy) perspective explained in english...look up http://handybobsolar.wordpress.com/ Check out the RV battery Charging Puzzle...it will answer a lot of your questions.
