Hi,
We keep our van at home, in the back garden connected to power. I run a small oil field radiator on low. With all the cupboard doors open and the bathroom door it keeps it the whole van luke warm. If the forecast is for extra cold weather I turn the temp up a little. The heat just keeps it feeling nice. I also run a dehumidifier on low. This collects any moisture especially after the van has just been used. I guess none is really necessary, but I think it helps keep it nice. We use our van all year round, so don't empty it. The small amount of heat ensures the duvets etc don't get too cold/damp.