Cover the skylights with either reflectix or closed cell foam same for the glass on the back door, I do my windows too at night. that will really reduce the heat loss from the TC and minimize the furnace cycling on and off. Secondly pack the area around the dump valve controls with fiberglass insulation as that is a major route for cold air to 1: freeze the valves and 2: let cold air up under the shower pan and into the basement. Leave all the inside cabinet doors open at night to allow warm air around the plumbing. I also put insulation behind the external storage compartment doors to keep in the heat and keep out the cold. I also add antifreeze into both the grey and black holding tanks to prevent freezing. I drain my fresh tank and use 3.5 gallon water jugs for my fresh water needs. Flannel Sheets and thick down comforters are nice, some folks use winter sleeping bags. Don't keep the TC too warm at night, I have it on low and it doesnt drop befow 58 while I sleep which conserves propane.
