Here you get a D&d Dice Box that has been designed so that you can insert round 8x2mm magnets.
This gives a secure hold of the lid for transport.

If you use flatter or smaller magnets, you can simply print a suitable spacer and glue it in place.

Tip: The magnets are best glued in place with a good superglue

Dimensions: 11,4 x 10 x 5 cm