Nice post, thanks for you ideas, it is allways good to see new ideas. I like your idea of using those small fan to keep air moving.
For the outside shower, I insulated from inside the camper with some expanding spray foam, Great Stuff. It does a nice job for puting a good inch all over you need more insulation and it completly block air intrusion. I also found that the propane box and the generator box was not insulated form the inside,it gives in the drawer compartment, so I added some foam there too. I added one inch blue foam under and at all sides of the water tanks and grey tank and installed Y type duct plus adding some ducting to direct heat all over in the basement, my TC has access from under the camper by some screwed plastic panels. I also added water line foam to every water line I could, especially does near the walls.
I relocated my batteries at the front of the camper in the heated compartment to keep them warm, batteries tend to have less power when cold.
Oregon must be very nice in winter, I was traveling there this summer.
Have a good and cozy winter!
I do too have the double pane window which greatly help.