I too have fitted a fan but I went for a 24V version that is used in one of our products here at work. I stole a "Turbo LED" lead from inside an old PC case for the fan connector, works a treat.

With regard to mounting, I mounted as empeg intended, all lined up with the predrilled holes. It is a bit tricky getting the top case back on but there is a trick:

Tilt the top cover up to 45 degrees and interlock the 2 clips at the front first (near the facia), Gently return the lid back to 0 degrees and you will just be able to get the back lugs in without putting too much pressure on the caps of the display board.

The 24V fan is almost inaudible (much less than the HDDs) and the temp stabilises at about 35 degrees.

Happy Happy joy joy.