This is my final rugged box design, I have made it generic with interchangeable inserts. I have included lugs on the base to allow the boxes to stack.

Locking lugs are provided for 2 small padlocks.

The latches and handle are ASA, the box is PLA with min 50% infill and 4 wall loops for strength. The hinges, handle and latches are using 3mm by 50 and 30mm bolts.  You will notice a 3mm hole in the top middle of the handle and latches, this is for glue to capture the thread.

I have included inserts for .223 AMMO with slots for 10 and 20 rnd mags. The top cover insert is to contain the smaller rnds from shaking out.

I also included a 30.06 ammo insert with spaces for M1 Garand clips.

There is a DWG file for the enthusiasts to create there own insert from a blank provided.

The gasket is TPU for air and weather proofing. 

A point to note: the print time for each component is quite long as the detail is for strength.