Two pieces that lock into each other by pushing. Each piece is secured with a cable binder (~0.9x2.2mm).

The lock is suitable for a box made from twinwall polypropylene sheets (Correx) of 2.5mm thickness. The design is primarily meant for inspiration because it probably needs to be adapted for your own particular needs (FreeCAD source is provided).

Print with PETG. (I did not test PLA, but PETG has much better elasticity while PLA is rather brittle).