If you have electric service get a space heater. We've been comfy down to about 28F in wet and windy conditions in our hybrid. I set the small heater to come on around 45 or so and the furnace about 40 (non-digital thermostat so it's hard to be precise). The TT gets chilly but not brutal - we like our feather comforter.
2013 F-350 CC SB 2WD 6.7PS
2013 Eagle Premier 351 RLTS
-SOLD- 2012 X23B
-SOLD- 2003 Ford Expedition 5.4, Bilstein shocks