Good idea, gnu. Balsam fir would smell good. The mattress is a thick normal one, and it's the warmest place in the camper. The water tank is under there and acts as insulation from the outside cold. It's the pipes between the tank and the sink that have frozen.
My cold is a viral infection from the sneezing audience at the concert. I usually don't eat public refreshments at concerts, but I was hungry. My mistake. Asthma makes an ordinary cold feel worse. I haven't had a cold for years.