Living outside Spokane, we got some snow this year as well (more than many earlier years according to the locals). I have since changed my "what kind of sissy spends so much work to insulate a bus.... it is already insulated, right?" attitude.
We ended up hanging sleeping bags over the windows in the back bedroom area, using 1 inch styrofoam board to cover them over as well in spots, and even placed it on the floor under the throw rugs to keep from freezing our toes. The bus was NOT planned out well for winter - a thing we will be remedying. I really wish I also had a 40 foot pusher or any kind of Crown - then I would build the home for the NEXT 12 months into that chassis. But lacking money to spend that way - I'll insulate better and re-modify the Bluebird I have.
One tip for cold weather - don't cut corners and be fast. I put salvaged kitchen counters in on one side - and on the other side put the 12 inch deep wall mounted counters (from the floor to the ceiling). THEN as the weather turned we realized we needed more insulation, and placed styrofoam on many wall surfaces. So - what is wrong? When you open the cupboard to get a can of soup.... there is no insulation on the wall that touches the back of the cabinet, and the air coming out of the cupboard is about the same temp as the open refridgerator door!
Still - it IS home for now....
p.s. This is when the snow was NOT that thick.... the next week we had over a foot on the roof but I did not want to put on snowshoes and trek up the hill for another picture!