I've been thinking about how to put 'living hinges' elegantly into a print for some time now. Finally, it sparked in the brain and I made it pretty fast in Fusion360: no need for support at all, elegant full closing box - first print turned out great! voila.
closing close up: https://youtu.be/EV_60fiUgbE
Other sizes should be adaptable pretty easy, but i didn't try yet. Comment and ask for other sizes If you want.
sharing is caring: Fusion file attached
0.15 layerhight, 0.4 nozzle