I was in North Dakota this winter in my camper. If you are going to be in one spot a while then skirting is the best option. Also try to park over the water/sewer connections like under a slide out, then put a 1500watt heater under there and you shouldn't have any problems with water or sewer. I also used a heated hose for the 3' that were going from under the camper to the hose connection on the camper and also packed some foam around that.
Inside open all the cabinet doors at least a little, run your refrigerator on gas and you must partially block the vent outside your refrigerator or it won't work when it gets cold, I mean -10 and colder.
If it's cold outside (again, cold) you shouldn't have any problems with moisture, but when it gets warmer, a dehumidifier is the best option once the ice inside your closets start thawing
If you have the camper skirted and a heater under there, I used plywood with blue foam over it, then you're ok to use electric heaters inside the camper so you won't use too much propane.
It's helpful to put an outdoor thermometer under the camper to monitor temps under there as well.
I also put that blue foam over all my windows on the inside of the camper to keep the frost down. I left a few open that got some sun though.