Just an update to anyone following my screen removal saga.
Yesterday I was determined to get the screen in question out no matter how may pieces and parts of the 345 I had to remove. Inside the aluminum window frame, top and bottom, are these plastic runners that are screwed to the window frame. I remove the two runners, lifted the screen, pushed out on the screen frame and out it came. It was as simple as that ! ! Didn't have to remove anything else.
Spring is in the air here in NH. We are working on our Airstreams and chomping at the bit to get out there. Hope to see some of you out on the road.