I made a lockable pistol case out of a ammo can I got from the armory at Cherry Point (a 9mm can, not sure if there is any difference from 45 cal).
I used some foam padding from a 40mm grenade ammo can (big!) to line the case as well as create a divider wall between the pistol and mags/ammo. I then put hasp base on so that the lid locking piece fits over the stud, so the stud sticks out through the locking "flap". Then I put a lock through the stud, and it's secure. I can use a rifle cable lock to lock the whole box to the inside of my trunk.
Kind of similar to the one that I had on my 45" WLA that my Papa gave me. It rode on the front axle and was to store ammo for the Thompson that rode the right fork. It was stolen from me in B'Ham, AL back in 1985. Damned Crackhead dopers! I just know my old bike became a crack weekend for some jerk!
I still have a can that is embossed:
The raised lettering is on both sides, and "REEVES U.S." with an ordinance bomb symbol splitting the "U.S." is on one end of it. I wish I could post a pic of it. Maybe my buddy will bring his camera over and I can do that.