Because the boat is in a large storage warehouse - I have to keep the
cover on ... when the boat is outside my house during Summer I use a
standard cover, the one on now is a purpose bought breathable cover ...
the manufacturer state it to be fully breathable ... i.e. no
condensation.

I have seen a couple of pictures in magazines of boats & classic cars
which are kept under covers and they have electric dehumidifers,
wondered if anyone knew of such units ... would need to be small not
household size.