Ender 3 Rear case duct
thingiverse
I modified the left rear case to house a 50mm fan instead of a raspberry pi. I would recommend using support blockers in the tight corner below where the fan mounts, I didn't and they were a pain to remove.
Download Model from thingiverse
With this file you will be able to print Ender 3 Rear case duct with your 3D printer. Click on the button and save the file on your computer to work, edit or customize your design. You can also find more 3D designs for printers on Ender 3 Rear case duct.