Winter Camping

We have boondocked in cold temps (upper 20's at night), rising to low to mid 40's during the day  - furnace runs a lot to keep things warm at night 60 degrees while sleeping.  Batteries will last 3 days for us (12v Interstate group size 24 deep cycle) before switching out to the other which is the same. Good idea to have a multitester or voltmeter - do not draw battery below 12.2v for maximum life of the battery.  When doing this we were winterized so no water in the lines so cannot give advice there.  No solar or generator usage.  Also since we would be outside during the day hiking or similar, the furnace would be shut off, saving propane and battery.

I've camped many times when it got down to 10 at night, and stayed below freezing.  I left it winterized and used the campground bathroom most of the time.  For 3 am bathroom visits I leave a jug of the pink stuff in the bathroom and flush with that.  Make sure you leave a window cracked open no matter how cold it gets or you'll create a sauna.

We camp all winter in the mountains where is goes down to -20C, -4F.  We generally heat the trailer with an oil filled radiator as it is silent.  As others have mentioned, crack a window and open a vent or ice will form on the insides of the windows.  Also bear in mind that the various plastic parts of the trailer get brittle in the cold, compartments freeze shut, etc. so you do need to be more careful with the trailer in the cold.