I have a 177 . The mattress is not very long, you should absolutely lie in it before buying!!
The furnace is VERY loud, cycles too often, and kills the battery. I highly recommend a small propane space heater if you don't camp using electrical hookup, and you can buy an electric ceramic heater for hookup camping, very quiet.
I use a propane Mr Buddy heater, and it is very quiet, and plenty of heat. On low, the one pound bottle lasts about 5 hours. In very cold weather (below 40), I have blankets, wool socks, a sweater, and 1 inch of foil foam board under the mattress for insulation. Using the portable heater means I save my batteries, and have a quiet nights sleep.