The screw in a cover you slide open and close would work about the same as the slides I was talking about. Same net effect. I can't really see your fan setup in the pictures you posted. If its that little box over the light at the end blowing down (or up?) I would say its to small and blowing in the wrong direction. But again, cant see. I just put a new fan in mine, a Dayton 4M217 but then again mine is much larger 
