Sounds like a good plan.
WE made one winter in a 30' 5er with a 13" slide. This trailer had two grey and one black water tanks. I also had a heat blanket attached to their bottoms and then had the tanks encapsulated with expanding foam. The trailer was a typical summer 3 season camper with R7 floors/sidewalls and roof.
I made inside storm windows from 1/8" Lexan and being set up permanent I used mobile home skirting.
I also wrapped the fresh water hose with a thermostat controlled heat tape and usual recommended insulation that goes along with it.
We had no freezing issues down to zero temps and 40 mph winds.
Biggest problem was interior sweating especially inside closets. We tried more fans....open windows and vents/etc but all that did was make a cold still wet, drafty camper with the heat going full time. We didn't git rid of moisture issue till we bought two dehumidifiers.
If we had top use a RV in the winter again its going to be one with a full time (real) 4 season package.
