The model includes cutouts for 15mm diameter magnets (x4). I used 15mm x 3mm magnets with a powerful hold (look for N45 or better strength for the best results).  Attach up to four magnets with some super glue.

I printed this easily with no supports at 0.42mm layer height with a 0.6mm nozzle for speed, and it turned out well for my use case. I printed it with the bottom on the build plate (pictured). 

115mm tall x 95mm wide x 65mm deep. Used about 90g of filament with my settings.