Unless you've done some setup, or at least research on dry camping, your furnace use could be very limited. It's one of the biggest power hogs in an RV, and will likely run your battery down quickly if left to its own decisions.
There's a permanent topic about boondocking / dry camping in the public lands forum, it provides lots of great information.
I would recommend a down comforter and/or cold weather sleeping bags for overnight, and then run the furnace in the morning when everyone is waking up. This way you can keep an eye on your battery level.
Keep a window and roof vent slightly open even at night, so condensation doesn't build up in your trailer.