I used 1/2" MDF , because it is what I had available. There are three pieces, two sides and one center section (with no rabbet). The two sides look the same, but they’re actually mirror images of each other so that the rabbet for the acrylic is on the outside of each piece.
Both pieces are identical.
2 things: First off, I figured that a coffee filter would be symmetrical across the arc; they aren’t. So be careful where you put the glue.
Second, getting the three pieces lined up so that the outside edges are nice and smooth is tougher than I expected. Take your time.
Once the glue dried, I sanded it and then painted the MDF.
I also glued these into the rabbets with an instant glue. Be careful with these as they fit one way but not the other (non-symmetrical filter issue again).
When everything was dry, I picked a bottom and put self-stick rubber feet on it, to keep it in one spot better