Spent 3 winters in an rv here in Eastern Canada. Nights are pretty standard at -10 to -20. Use a small wood stove for your heat, with a propane furnace backup because your fire will go out while you sleep. A programmable thermostat can be used even off grid. Maximize your use of "Reflectix" insulation, primarily as window covers, and additional ceiling insulation (your heat all rises). Floors must be spray foam insulated (a horrible job but an absolute must do) to prevent frozen feet. The best case for condensation is using wood heat and above all else ventilation. Yes that means Crack a window open in the winter. Moisture in your walls comes from the interior so if possible use a vinyl coated wall board or a Reflective vinyl vapor barrier behind your wall board. Other outside wall moisture comes from leaks. R5 foam is no roaring hell in the winter so Reflective insulation which will return up to 90% of the heat loss is a much better deal. The most important thing to consider is ventilation that allows your heat to dry the air and is essential for a wood stove. Do not rely on any open burning propane or electric, you will freeze.
If possible skirt the vehicle, even if it is only with tarp material on a frame. Do Not use straw bales. THESE ARE MOUSE HEAVEN. They usually come with the mice already housed, and they will come looking for you. Find a way to double glaze your windows (think old style storm windows). Small computer fans can be ceiling mounted to even up the temperatures. Best of luck. As a side note, make sure all your plumbing is inside the heated space and not under the floor.
