On the photo you can see the original part (white) and my design (black). The handle of one box was broken, so I made a quick replacement part. Maybe this will help someone else, too.

If you want to tinker with the design, it’s also available on OnShape: https://cad.onshape.com/documents/28b10ffba52aa4743779f946/w/87fc606044225b16fe17d3bf/e/ac421a55e7adfbd1ffedf0a1

Printed in PETG with 3 perimeters and 20% infill for stability.