This is a box-generator that generates rounded-corners boxes, requiring no supports to print and no screws to assembly. You can add feet for a PCB board, and custom holes for displays and buttons.

You can customize it following the comments in the header of the two examples provided. Open it in OpenScad if Customizer didn't work. It is easy even if you have no prior cad programming experience.

If your customized box is larger than you bed, split the box and bottom cover in your slicer software. The box should print with its top faced down, i.e., the top of the final box will print in the bed surface for improved appearance.