There are only two cures for condensation Andrew, extraction or ventilation. Since extraction isn't really an option try sleeping with a window or two in the vent position(I presume you have this problem first thing in the morning), and if you have blown air leave the fan running all night to encourage air circulation.
Leave the side window accross from the bed on the night catch. Leave the sunroof also on the night catch.Leave the fire on 1000watt all night with the thermostat set half way. We find it better not to use the blown air. We have a Senator Wyoming and caravan through the winter. By doing what i have suggested we never have condensation even in really cold weather. If the van is too warm do not turn the heater down but put another window on the night catch. Good luck.
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