I made this trip successfully in between the two major February snowstorms in the mid-atlantic states this year. I brought the drop light, but did not use it. My plan had been to plug it in one of my camper outlets and leave it in the bathroom cabinet. My camper has an inverter, so I have 110 power available as long as the camper is plugged into the truck(while running) or on the deep cycle.
I ended up buying a cheap wireless indoor/outdoor thermometer at the hardware store before I left. I put the transmitter inside the 'outdoor' shower cabinet, kept the reciever with me in the cab while on the road, and by my side in the bunk. I figured that would be the best indicator of the temp in the wall of the camper. With the furnace on about 68-70 degrees, and all the cabinets inside open, the temp never dropped below 40 degrees in the wall. We had some days that the outside temp was in the teens but never below that. Coldest night was 21 degrees in FLA, but not long enough to freeze up. Even without a cold weather package, the Lance camper is pretty airtight.
In the end we stayed 12 nights below North Carolina, and all but two had dropped below 32. We had no freeze ups, but did have to top off the propane once along the way. I carry two 20lb tanks, and I used almost four during the trip. It was worth it to stay comfortable and for peace of mind.