I remember someone keeping the pop top down, for over a week and then were surprised,
when they had mould under the beds!
Warm but well ventilated is the rule but under the seat boxes it is cold and where the back
of the seat cushions meets the caravan wall. I was thinking about using battens to keep the
cushion off the wall as while we were in Norfolk, the windward wall always had condensation
on it. Then I saw this http://www.millbrook-caravan-mattresses....-range/dry-mesh
Pinned up the wall behind the cushions, it would allow air to circulate.

we move the bases forward about 1 inches to allow draught, the blown air heating does help to warm the areas under beds as the pipe get slightly warm
you could add a vent to the front of the bed boxes in a discreet place for extra circulation