Winter living In Wyoming

You do need to enclose the lower part to help keep out the wind and snow. Have seen various types of enclosures from hay bales (not the best in case they catch fire) naugahide skirting, to fully built walls of plywood W/ 2x4 studding. Probably the best is the styrofoam sheeting with proper supports to hold it in place. The kind that has aluminum foil on one side. With the under side enclosed you can use elect. heater underneath to help when it is below freezing. We have put reflex insulation under our mattress. Do not close up the 5er too tight or you will be having frost problems inside from cooking and just breathing so leave a vent cracked or window slightly open to let moisture out.
Have lived here all my life except for when we are on the road seeing the West.