An inexpensive yet effective way to create port screens is to purchase the window shades for automobiles that are made with a plastic side that clings to glass on one side and a UV resistant screen that provides the shade on the other side, like these at Amazon (4 shade screens for$14.97)
I just cut out the plastic, stitched a button in the middle, and attached thin shock cord to the button. All my ports have something (like a mushroom) just inside that I use to tie off the shock cord. The frames are so flexible you can ball them up into a bag, and the screens are too fine for no-seeums. Mine have lasted years in the sun.
