120mm Fan to 100mm Duct with 12mm Magnets for attachment

I have a 120mm fan in my window which works as both an extractor fan while soldering, and generally helps ventilation in my rather stuffy room. However I don't want to block the rest of the window up, and when using it as an extractor, a large amount of the exhausted air blows straight back inside. In addition i'm in a rented house so I cant make any permanent modifications to the window, which is covered with fly-screen. So I came up with this.

Superglue a 12mm diameter magnet in each of the