We insulate all our Tiny House RVs using closed cell foam for the walls and roof for the rigidity and R-value, and rigid insulation in the floors. This gives you an R-value of R21. You will still need to add insulated skirting around the trailer chassis, to regulate the temperature shift below the trailer chassis. We often have some recommended upgrades for those living in extreme winter climates. For example we often recommend adding in a propane forced air furnace, or upgrading the mini split to an Arctic mini split (220V) to better withstand the cold climates. See our free Cold Climate/Winter Guide for more detailed information.