You have one amazing setup with so much reserve capacity. Thanks for sharing!
We too dry camp most of the time with a rare oppertunity to plug in. I considered a solar panel (or two) and 6V batteries, but decided to keep things as-is for cost and simplicity.
We replaced our 3 year old factory original batteries two months ago with a pair of Walmart's biggest (with the yellow label), which just make it in the tray. For how we utilize facilities, they held up very well during our three week trip in August. I do suppliment charging. You can read more about my charging and power consumption story here:http://phoenixusarv.com/community/index.php?topic=73.0
Keep in-mind our rig is a 2007 with the earlier Tripp-Lite invertor.