I thought that as we're not using the van in the winter months and it's parked up at home I'd run the heater for a few hours every month or so during the damp winter season. Might just keep damp and mould at bay.
Never heated the caravan over winter as it was in store or being used. Just ensured good ventilation and opened everything up, and put furnishings on their sides. Prior to winter all surfaces had a wash down but never used spray polish or the like. Was never affected by mould. But western Scotland could be different given its propensity for wet stuff.
Good ventilation is far more important than heating. I have never heated any leisure vehicle over winter for 20+ years, but I have always ensured good ventilation. Never had any mould etc.
I believe the constant warming up and cooling down creates an environment conducive to mould growth. I too have never heated the caravan in winter storage, only when we use it.