|Do you have ports like this?|
...you can easily make and fit storm windows for them too! I don't take credit for this idea - it came from Drew, 6 years ago.
But in any case, it couldn't be simpler. First you need to remove the screens from your ports (we don't have ours installed - no bugs to speak of in the PNW... :^) ). It is easy to do this. The rubber gasket that traps the screens in place is not glued in - it is just wedged into a slot on the port frame:
|Just pull it out|
You just need to pull it out. If you haven't ever had yours off, they may be glued in there with algae and other growth tho. With the gasket off, simply lift the screen out of its recess.
Of course, you'll need the actual storm windows. For these you'll want some kind of thin plastic - less than 1/8" (the thickness of the screens). I made mine out of the glazing from a couple of old poster frames that were destined for the recycle bin. I just traced the outline of the screen on the plastic sheet and then cut them out on my bandsaw. I suppose you could use a sabre saw, or even a hack saw (tho the corners would be tedious). And you might even want to smooth out the edges with a bench grinder and/or a file - I did this with mine.
|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.