Bought the Solarventi unit for the cottage, and I am just waiting for delivery

I got the smaller unit in the end - it's the core of the cottage that
gets most damp, and the 20 m2 unit should be enough to deal with that.
Anything The race now will be to get it fitted before it gets too damp
up there.

Northumberland is the officially the coldest county in England, but it
does average 1350 hours of sunlight a year, and that is 1350 hours of
dry (warm(ish) air being drawn into the stone caravan. And some of
those hours occur in the winter. Honest.