Many years ago I was having condensation problems in Rum Runner. I wasn't  
satisfied with the amount of air the Nicro vent moved so I made my own using 
a  12 volt case fan from a computer. Attached is the drawing I made at the 
time to  explain to the list what I had made. It worked very efficiently and 
eliminated  my condensation/mildew problem completely.
 
Rummy