Hello All,
I am posting this message in case it helps someone. We have made a 3D printed enclosure for the Nextion 3.5 inch display. For the 3.5 inch bezel we used the same basic design that is downloadable from the Nextion website but modified it so that the four outer holes go all the way through the bezel so it can be screwed to the enclosure without first drilling out the holes. The enclosure has mounting tabs with holes so it can be screwed to a wall or inside a larger enclosure. Feel free to download the STL files for the box and bezel. If you find it useful, you can buy us a coffee if you wish 
Regards,
Download Link:
https://remotemonitoringsystems.ca/projects/touch-display/touch-display-project.php
