Originally designed because my girlfriend is slightly allergic to cat dander and our previous Corsi-Rosenthal was looking a little ragged, this entirely 3d printed frame is designed to hold 4 20"x20"x1" furnace filters in a standard Corsi-Rosenthal configuration with a box fan set on top. I would also recommend using some ½" foam weather sealing strips to both seal against the fan on the top of the model and as feet on the bottom so that it doesn't rattle.

You will need:

• 4 x Mega Corsi-Rosenthal - Bottom Corner
• 4x Mega Corsi-Rosenthal - Top Corner
• 8 x Mega Corsi-Rosenthal - Horizontal Middle
• 4 x Mega Corsi-Rosenthal - Vertical Middle
• 8 x Mega Corsi-Rosenthal - Vertical Clip
• 16 x Mega Corsi-Rosenthal - Horizontal Clip
• 4 x 20"x20"x1" furnace filters, the higher the rating (within reason) the better. Higher ratings will need to be changed more often.
• 1 x 20" Box fan. Save the box to make a shroud on the top and to fill in the bottom of this frame. See original Corsi-Rosenthal instructions for more details.
• ½" foam weather sealing tape

I do not remember how long this took to print but I do seem to remember the frame segments took a whole 1kg if not more. All of the black components are PLA and the orange are PETG, though I do not think it matters and all were sliced at .2mm layers as fast as I could get them without any supports. 

This model was designed in Onshape and is accessible for modifications here.