Woody, your questions made me pull out the manual/handbook to look up a few things. Ours also says the AC fan can be run on
12V. We have never tried this, but I intend to, next time AC is needed. All the other fans in our 05 run on 12V, so maybe.
Our battery switches by the door operate independently of each other.
Our owners handbook has both diagrams. If you can find a manual on-line, they are in sections H & I. I would be happy to send copies to you, but I'm sure other posters have mentioned finding copies on-line.
We HAD a 4 speed fan on the engine heating & AC controls. Then we had some work done on the defroster, replaced the hoses & we now have a 3 speed fan. The mechanic was puzzled, but on ours its the small dot that is off. Still does the job.
Re: your shower idea….have you considered a portable shower stool? If your shower is like ours, there is room on the floor, next to the built in bench.
By the way, did you ever build the cabinets for the area by the dinette? If you have, I would love to see pictures.