@MAF, my husband and me are stranded at the moment in Evanston, WY. We are in our t@b. It is approx 15°F. We did the best we could to winterize when it became clear this would be an extended stay, by draining the lines and using a small 12v air pump. This is an unexpected and emergency circumstance, as the transmission of our tv has failed. We use bottled water inside, and are using the toilet as suggested, flushing with rv antifreeze. We have been here for 9 days in this weather @ approx 7,000 ft altitude, sitting inside the t@b, parked at a "closed for the season" rv park. We have 30 amp electrical service for the alde. We take "sponge baths". We are not putting any water in the gray tank, as our supply of rv antifreeze is limited. If 9 days, so far, in these conditions is not winter season camping, I don't what is. It has snowed twice; but at this altitude with low humidity, it evaporates quickly. We have had to empty the black tank twice, making sure we work the antifreeze into the gate valve afterward. Don't know when we'll be back on the road heading home, already feels like we've been here a very long time. This wouldn't have been financially survivable if it weren't  for the t@b. 4 seasons, easy peezy.

 As promised here are a few pictures of the instillation process. I only took a few pics so sorry if this is a bit incomplete.
I first removed the protective plastic corrugated cover which protects the grey water, fresh water holding tanks and the associated plumbing.  The next task was to extended the Alde system by taking the outgoing hose from the passenger side (under the seat) convector, see below and 



then drilling two holes into the floor (gulp...) and extending the system to the holding tank area, then ran the hose system forward where I mounted a "mini convector" (thank you Alde!) in front of the fresh water tank and beside much of the fresh water plumbing.  See below.


Next had to seal all of the holes in the frame, this was done using sheet aluminum and construction grade adhesive.

I then attached aluminum L shaped flashing 3"x4" to the bottom of the trailer frame with the four inch side hanging down, see below. I drilled a small hole and used self tapping screws for this process.  Were I to do this again I would use the three inch side to hang down there by saving an inch of clearance.




I took another piece of flashing and installed with the four inch side to the four inch side (hanging down) so it created the channel for the insulation to sit in.  I used pop rivets for this process. See the left side of the pic below which shows the channel.





Insulated the sides of the frame with standard house wall insulation and then used 3" Rmax Thermasheath (R20 value ) foam paneling from Home Depot cutting it to size and fitted it in the channeling enclosing the entire bottom of the trailer.  Also used aluminum foil tape to seal the joints. Also had to create a trap door for the fresh water tank drain. Sorry some mud on this pic from the test trip



Finally the project was almost done




The project is complete (see the cut out for the trap door above) and this is what it looks like fully enclosed with the plastic corrugated protector reinstalled over the insulation