It does not work well. The dramatically reduced airflow means the fan is working hard for basically nothing.

However, if you are gunna go through the trouble of making a cube anyway, you can make one out of thin strips of wood or laminated cardboard, and attach washable air filter material all around it, and you never have to rebuild it or replace the filters. Just wash it with a sprayer of some sort (hose, shower, sink) once every few months.