Mine has 2 drawers, one near the top and one about middle and they are solid so I know they don't circulate at all. From top to bottom I can have a difference up to 10% rh, depending on how often I run the fans, which is why I want to hook the fans up to a timer instead of the humidifier.
My fans are placed between hanging over the edge of the shelves between the door and shelf. They are not permanently attached but I'd like to get to that point.
I was thinking(too lazy to attempt yet) that I would cut some slots in the drawers to allow for circulation similar to shelves/trays in normal humidors.
I have like 3 lbs of beads on different shelves to help level everything out...I got the tower super cheap...and got what I paid for...but it works, with work.