We use Eolian all winter long (at the dock anyway), therefore we heat her all winter long. On houses, storm windows are used to provide an extra layer of insulation against the winter cold and weather. If you have ports like these:
|Do you have ports like this?|
|Just pull it out|
|And just slip them in where the screens were|
And then you just drop them into the recess that the screen was in, and reinstall the rubber gasket. (If you look closely, you'll notice that there is a joint on the gasket - this should go to the top.) Be sure to get the gasket flange firmly pushed into the slot all the way around, otherwise the window won't close - you could break it if you try.