We went through our TC and put reflectix under our bed and in all of the cabinets near the bed. We also put in reflectix in our windows. We also use it in all skylights and vents. The vents/skylights fit are cut slightly larger to fit tightly. The windows are cut to be held in place by window frames or curtains.
I'm not sure about backdoors not being insulated. :) Ours is solid insulation foam except for the window. We use a reflectix attached with velcro over for that.
If you do use plug in heaters, keep in mind that it won't heat the basement which is not a problem if your TC is winterized. We've used RV antifreeze to flush. For sure, reducing the temperature a little will help decrease battery usage. We found like others hear that a digital thermostat seems to control the temps better and the bonus is the LCD display with actual temperature.
I have an adjustable fan electric heater that's made for boats to vary how much heat it produces and how much fan it uses. We also have a heating element for the AC.
