My brother likes the Gridfinity box I printed, and he wants a car electrical connector box with custom dimensions.

I copied the basic design I printed before:

https://www.printables.com/model/495142-rugged-gridfinity-box-parametric

Using my Voron 350mm printer, I printed with 1kg of black Eligoo Rapid PLA+ material at a 20% infill rate, without the need for support structures. You'll also need 6 M3x30 screws for the hinges and latches.