I built the PTC heater for my Mono but I needed a clean way to run the wires out to the power supply. This is a minimal riser that has a 1" gap in the back to allow wires to pass through. You can improve the seal by adding foam, batting, hot glue, whatever you fancy. I left mine unaltered and the seal is very good, the temps hold well and the noise is significantly less than when I just had the cover haphazardly placed over the wires. I printed in PLA, you shouldn't need to print in anything more temperature resistant as the enclosure only really needs to be about 80 degrees F. The riser will just barely fit on an Ender 3. You will need supports for the lip. You may end up adjusting the size slightly. Shown in the images is the pervious version that needed a slight depth adjustment. Current iteration should fit but is untested.

Ender 3

No

Yes

.28

10

Supports needed for the interior lip. Should just fit on an Ender 3 bed with no brim.

Designed in Rhino. Many versions and 3 prints later I had a riser that worked. It was difficult to nail down the measurements exactly so there was a bit of trial and error.