I had a great big screen with magnets in the hem that went all around the windows, and was baggy enough that you could open them. I found that even with the windows open there wasn't really enough airflow with the screen in place, and if it got cold at night the screen would catch the condensation and let it drip inside. It wasn't ideal. In the end I replaced the front windows with sliders. (And then switched back to leaf windows when we bought the caravan).