Any question answered...

Or try one of these: hgldirect.co.uk/ekmps/shops/g­rowthings/images/compact-dehumidifier-mo­isture-absorber-2267-p[ekm]296x296[ekm].­jpg You can pick them up in £1 stores. I keep one in the bike room (because I'm a tart (and we have stupid breezy sash windows))

If there is air circulating from outside you're just trying to dehumidify the world, which might take a while.

If the room is well sealed - plastic windows without vents, a door with no gaps around it - then a dehumidifier could be beneficial, but if the windows are breezy then you're better opening the door and getting a through draught.