To make the cutting of the plastic a little easier Take a hack saw blade and scrape the outline several times,, The dust will not get in the fan! After you made a deep scribe take a NEW SHARP Razor knife and cut slowly in a rocking motion! I didn't want to chance using a heat gut or hair dryer in fear of warping the plastic ! BUT in the end well worth it, If you have the cable on the side of the box door to slow the opening tie it off with a string so it does not retract, can be a pain to retrieve ! After you first filter you will say Holy **** look at all the crap lol