I asked thor about the house battery which comes from the factory and they sent me a few details on it. It looks like this thing is only 35AH which seems very wimpy.
I examined the battery tray and it has an upward lip on each side which limits replacement battery sizes quite a bit.
I've searched for a replacement (much higher AH but still fits in tray/space) and this is what I've come up with:
VMAX MR197 12 Volt 200AH AGM
The measurements all claim that it will fit and since it is still 12v I don't have to make any modifications. It looks like all I have to do now is just make my purchase and swap the batteries but things are never as easy as I think they will be. I know I'll need to run the generator for a couple of hours before driving anywhere to prevent the alternator from working too hard to charge this sucker. Can anyone see anything else I missed?