Where is the MacBook Air (13") Mid 2012 fan exhaust? I would like to put a plastic dust cover on my MacBook Air, but I'm not sure whether it would obstruct the fan exhaust.

Below is a drawing that shows the soft cover.



I know someone that would make it for me from the material in those plastic bags with zipper, like the one below.
It should be directly in the back, toward the bottom (across almost the entire machine). Look for the black plastic strip across the back.