Having any sort of humidity control in a screen cage will be difficult. Your humidity will be high in the direct fog stream, but with dissipate quickly. To get humidity control in the cage you have you can put window insulation film over the sides, back, and front main door. That will allow your fog to stay in a little more, spread out, and you can raise the humidity of the environment as a whole. You may even have to block off much of the flip up service door. But you do want some screen at the bottom front so cool air can come in, heat up, and rise to give you your airflow. Being directly in the fog stream can be a draft and uncomfortable for a chameleon. Having a general high humidity is the goal. Here is a video on how you can turn your screen cage into a hybrid cage for under $10.
Here is a link to the window shrink film
Window shrink film