The best way to eliminate dust buildup is to not have a dusty room.

It also helps to have the case sit on the desk instead of the floor.
200R has lots of openings where air can get in without being filtered. In particular the top is completely open.
You could make it relatively dust proof by first adding a filter for the front fan, then installing another filter and intake fan on the floor. Now you have two fans blowing in, and one fan blowing out, resulting in a slight positive pressure which, in theory, helps eliminate air getting in through unfiltered openings. Finally, cover the top openings with something, e.g. magnetic filters, or you can conjure up some DIY solution.