I've attempted to attach a before and after photo of this project. The single interstate marine battery was replace with two Vmax 6v golf cart batteries. Because the new batteries are AGM (sealed), the vented battery box could be removed saving lots of space. The two new batteries fit with no trouble at all. I think there would even be room for four of these, but that would be another 130 lbs of weight.
So the finished mod is:
2 Vmax 6v GC batteries $500 total
1 Progressive Dynamics 55A converter $200
1 300 Watt pure sign wave inverter mounted under the dining table. $230
1 master cutoff switch $20
So about $1000 total and about 5 hours of effort to make the rig boondock ready. Solar would be nice, but we'll leave that for next year.
I can already tell the new charge converter a big improvement. It has a blinking green led that tells which stage of charge its in, plus an override button to force a stage....handy when the generator is connected.