One could greatly improve ventilation by leaving all portholes open during the week. However rain will find it's way inside and really "dampen" your effort of drying the interior. A Nonsuch owner introduced me to a kind of eaves trough (he called them eyebrows) that mount over the top half of the opening port holes to keep the rain out but letting air in to ventilate. Available from any chandlery and WEST etc. Not cheap, but works for me. George of Scaramouche