I posted this info a while back on how I keep the TM warm and use two space heaters.
"We have only camped a few times in the cold, but mid November in the low 30's was the coldest. We used air conditioning foam (gray from hardware store) under all the flaps. For the large flap up near the front, we used leftover pink foam cut out of two large pieces to insulate that area. It's hard and we cut to fit in the space. We a 1500W twin ceramic heaters we use for heat in the main area. I also have two 200W small space heaters we use for the bedroom areas. When taking a shower, the 200W is nice to heat up the bathroom. Remember that there will be quite a bit of condensation each day to deal with. Mostly in the windows. We haven't been braved a trip longer than 3 days in cold weather. We did not have hook ups, so didn't need to worry about a hose line freezing. Good luck!"
Since I posted this, we just upped the 1500W heater to this model
http://costcocouple.com/bionaire-dig...-tower-heater/ which works even better than the twin heater we had before. We put on the counter above the fridge and let run all night long and it is programmable, oscillates and worked great. We still use the 200W in the bedroom on the TV shelf that came with our TM.