With the varying air quality over the past 2 years in the PNW one of the suggestion was to combine a 20" box fan with a high quality AC filter (MERV 13) to help reduce particulates in the home. Last year we went low tech with zip ties. This year I created this pretty simple clip. Hope this helps for those that can use it.
This is a link to a UW professor showing how to do the same with duct tape - https://twitter.com/uwnews/status/1414973140241817600?s=20
As requested below here are some pictures, the filter can go in the front or the back, not sure if one is better than the other and may be dependent on where the switch is at. This first image shows the arrow on the filter indicating the direction of the airflow:
Below are front and side views: