The model  is pretty good https://www.printables.com/model/757059-multiboard-push-fit-vesa-bracket-and-raspberry-pi- but the mounting bars are not at multiboard spacing, so you can only use either the top or bottom row, using a raised mid hole multiboard bolt.

This model replaces one of the bars, so the can fit flush. 

You will need 2 M3 bolts at least 20mm long. 

Print 2 walls, 15% infill - but it's not too fussy.