Have you tried a towel over 1/2 and a quarter of the screen top on the tank? Just enough to let fresh air flow in while letting the other stale air out. Spraying without the screen top(I use reptibark so I spray until the bark changes into a wet look this keeps my humidity for a good 4-6 hours depending on how hot it is in my room(which is usually a good 80-84F)
I have also heard of people using styrofoam cut into shape over the screen and around the sides of the tank to insulate it this seemed to have helped them if no styrofoam try a blanket or towel. I have also heard cardboard can work as well. Just make sure the noodle has breathable air and that there is enough space for the air to filter out.
There is also a sprayer from Exo Terra that you can set to spray consistently and if you have a herp-stat or similar model you can set it to maintain a certain humidity.