Dianne, that is a great post and so very detailed. I'm sure it has and will continue to help so many people with questions.
We are now on our 3rd winter, living full time in our Carriage Compass Fifth Wheel.
Many trials and errors and felt that we finally got all our ducks lined up. 2 Winters in Osoyoos and now we are in the mountains of southern British Columbia along the Boundary Country. Minus 23 one morning (celsius).
All our neighbours had frozen pipes, hoses, water lines, etc. We were feeling pretty great about ours not freezing......BUT...when we went to pull the gate valve on the grey tank..it would not budge! First time in 3 years. So we put a small heater under the skirting on 900 watts. After about 3 hours, the temp rose enough to pull the valve. Same thing happened the next day, only with the black tank. So, confused about this. After 2 winters without it happening, and then boom, it did.
But at least we have a method to take care of it.
We have some videos on our youtube channel about things to do to help your rig survive the cold if you are interested.
Getting through the Winter in your RV