By using a low wattage heater ie 55w to 100w the temp inside the van is only kept a few degrees above freezing. 5 deg to 8 deg is the perfect temp as moisture traps and dehumidifiers don't work below 5 deg also below 5 deg moisture bags just fill up in no time as all the air is damp.
Also fit winter fridge vents and ensure as much air from the outside is prevented from getting into the van.
BY not causing a wide temperature swing inside the camper ie high wattage heaters this does away with condensation when coupled with and external screen on the front and blinds and curtains pulled. Handy also to leave all internal doors open cupboards etc
Wide temp swings or campers just left over winter with nothing do the most damage.
Everyone has their own view on this subject
all I can say is we have no condensation and no swelling of joints , panels etc so it works in our case.