Well, I've dug in, mostly by making my bank account complain from all the purchases so far.
The first investigation into the walls was a nice surprise, pulled the old water heater, absolutely no water staining at all around where it went in. Wood still looks new. Hopefully get some photos posted later tonight.
Discovered that sadly, I'm in the same boat with the water heater upgrade as I was with the KIT. The older units have a taller front and box, which means I'll need to add a 1x2 to the bottom sill and then metal it over and seal it so that the water heater fits in snug.
Off to the hardware store again tomorrow to invest into wire so I can start wiring in the new charge circuit before I put the water heater back in place, as the plug wires will be coming though the wall right next to the water heater.
