I have one of those boxes that I installed in the saddlebag of my Harley, but the cable is way to tiny to rely on, as it appears to small to withstand a decent set of wire cutters, so I drilled the back and used bolts to secure. I think this has an application for confined space, but not for an auto.I have in my car a Gun Vault, comes with a steel cable taht I have around the trunk frame, but fits under the seat also
Will never leave the gun overnight
Something more like this would be a better solution, and is the same price. I have had one in the house for a couple of years, and it works great.
It could easily be bolted to the floor in the trunk or other location, and would take quite an effort to open, much more than the little gun box.