there are a few options. if you dont want to look out when the ports are closed get some self adhesive frosting. another cheap option if you can sew is a cloth cover with either elastic or draw strings. or even easier is some cloth pieces with some velcro sewed on and some velcro patches above the port, and you just stick them on when needed, its what i am doing.
Don Casey had a good idea in one of his books. Glue two wooded drawer pulls to each side of the port, run shock cord with a loop on each end thru the top of the curtain. The loops fit over the knobs, inline with the hinge. Undo one loop, open the port(or close) and redo.
On my boat I have window inserts made of that foil-covered bubble wrap insulation, and they do excellent double duty as a privacy screen. They block light and views entirely if that's what you're looking for.
Just get a roll of the stuff, cut it to fit in your inner window sills (adding a little extra to make sure they crinkle in and stay put), then just stick them in when you want them and store them when you don't.
I bought some fabric and found a lady on Craig's List to sew some simple curtains for me. She sewed a 3/4" pocket on the top for shock cord to run through and hemmed the edges. I bought some small C clips (don't know what they are called) from a rigging shop and ran the cord through them, and tied knots on each end. If I want to open them, I tuck them up into the shock cord. Simple, effective, and the whole deal probably cost me $100.