I need to add a case fan (probably 120mm or possibly one or 2 80 mm fans) to the case window on the side of a Lian Li PC65 in use with my Mach II. I want to get better airflow over the memory and vidcard.

What's the best way to cut a hole in the window? I want a clean cut. I have a dremel but fear that with the window (works fine on aluminum!). Do you guys suggest a hole saw? Mask off the window first before cutting, etc? Just looking for some tips please & thanks in advance.