I remixed this to make it printable without supports. I also modified it so I could tap it for 3mm screws instead of using nuts to attach the pieces together and to mount the fan.
as JonBAL said in his original version, which is very good by the way, this provides a major upgrade in cooling the electronics box. It was quick and easy. I mounted my fan to pull air out of the enclosure but the choice is yours.
I printed my backplate with no top layers just because I liked the honeycomb infill.
After printing I sized the holes to 2.5mm and tapped them with a WARM 3mm screw. Do not get your screw to hot or you risk melting the holes out, I did that on another project.