After I retired out of the military, I picked up a Secureit Fast Box
and used a quick release cable mechanism I MacGyvered (The whole safe
can quickly be removed from the vehicle, but the quick release can only
be unlatched from the inside of the safe.)
It has a cut resistant cable bolted to the vehicle's frame. I also
added a red motion activated LED system with redundant LED's and power,
so when the safe is open in the dark, I can see my gear inside.
This is just a great product. The world has no shortage of violent
criminals and car thieves. At least I don't worry much of the later,
as a car thieves generally just smash and grab. Breaking into these
fast boxes takes a lot of time and trouble. A testament to how rugged
these boxes are.
Its a great product, easily fits all my gear and has served my needs