i have used my '92 dry (no water) down to the mid teens.
very comfortable. be prepared to use alot of propane, as you well know living in the great white north!
condensation is a problem, ice can and will form on the windows. you can leave a vent cracked open during the warmest part of the day. this helps vent the moisture. then you can close up again at night.
if you do plan on having water onboard, make sure you have all the needed things to winterize in a matter of an hour or so. just in case your furnace quits or you run out of propane.
propane, carbon monoxide, and a smoke detector are absolute necessitys for safety's sake!