Bought a house with a screened in porch, what is the proper window setup? Current one seems to be a shortcut to mold.

Just bought a house with a screened in porch, here is the setup:

-wooden structure with wood roof

-1 side is the house, 3 sides are almost floor to ceiling screens and 3 screen doors (one on each side). There is about 2 feet from floor up of wooden wall except at the doors.

- the current window setup is screens with bamboo blinds on the inside and plastic sheets stapled to the windows on the outside

- the floor is this outdoor carpet

It's really musty in the room... what's the proper thing to do? I plan to remove the carpet. But what about the windows? Surely the plastic sheets are not a good idea as they keep humidity in and prevent airflow. Is there a reasonable reason to keep them? Is it a seasonal thing? Basically, how do I maintain this screened back porch?