Burl, we are far from tired of the 213 :). Because of all the 'growing pains' it had and all the mods/fixes I have made, AND 'cause I love that Chevy engine, I don't want to give it up. I like your ideas. I my wife will be upset about giving up the sofa, but it actually is a space waster (now that I think about it, I wonder how far it projects out from the wall in the upright position?). I think it's time to crank up Google SketchUp!!!
I have a single house battery. (12 volt Gene?) I always wanted to add a second, or switch to 2 6 volts, but the problem is room and a stupid access door that doesn't allow much access at all. Adding water is an excercise for a contortionist. I once took the whole thing down to service it.
Keep those ideas cooking!!!