Redesigned box with hinges and latch. Printed at 15% infill with just a little support on the bottom part on the latch. It may work without it but I didn´t want to take the risk.

EDIT: For some reason the older files were mismatched and had different hinges. I fixed the hinges and these two parts fits ok now. (Not compatible with either one of the older parts).

I've included the sketchup file if someone wants too see/modify anything.