I've just bought 2 of those cheapo Argos fan heaters for me and my sister. They seem too good to be true for the price, but others on here have recommended them so I'm hoping they'll help us fend off some of the Norfolk chill over Easter.
------------- 2019 trips booked so far:
Easter - Red Shoot, New Forest
May - Secret Campsite, Sussex
With regard to heaters and condensation, this is all relative to the dew point of the air. This is the maximum amount of water vapour that air can hold at a given temperature. The warmer the air the more moisture the air can hold on to.
So, yes, using a heater will warm the air and reduce condensation. However if the walls of the tent are cold, which they probably will be if you need a heater in the first place because of the outside temperatures, then as soon as the warm air contacts the tent fabric then condensation will occur. Especially if you have people in the tent breathing out water vapour and possibly damp kit which you tend to have in the colder months.
In effect, if the tent fabric temperature is lower than the dew point of the air then condensation will occur. It's unavoidable. You could also argue that by not using a heater the air would be cooler, so in theory cannot hold as much vapour meaning condensation occurs more easily, but if the air temperature is lower than or equal to the tent fabric temperature then condensation will not occur!
------------- May 2015 - Arrow Bank 4 nights
July 2015 - Manorafon 4 nights
August 2015 - Piccadilly Caravan park 3 nights
August 2015 - Wheal Rodney 11 nights