Due to a couple of private messages, I am more fully detailing this system.
It is a product called "Advanced Security Products LLC. GunVault". I got it at my local gun shop for a hundred bucks. It is all metal, with a key and electronic locking mechanism. It has buttons, so you can enter your own code to open it in a hurry, or in the dark, and it has a key for when the batteries die.
I located a spot in my trunk that was relatively level, and did not interfere with the spare tire stuff on the bottom of the trunk. In my car (Subaru Impreza WRX) that is off to the right a little bit, so I mounted this safe to the left.
Be aware of where your fuel and brake lines are before mounting this- you don't want to drill through either of those things. Also, if your fuel tank is directly below the trunk, make sure there is clearance, you can access the bolts under there, and that you won't drill into your fuel tank. You should be able to get under there and see if there are any potential hazards.
It came with a template, which I cut out and laid on the carpet. I cut the carpet away to reveal the metal and soundproofing material. I put the template down on the metal/soundproofing, and used an awl to mark the drill points. This particular safe has 5 holes for mounting- two at the back, and three at the front.
After marking the holes, I drilled them with the appropriate size bit I had for the bolts I had on hand. I used smooth head bolts, and ran them up through the trunk floor into the safe, and screwed the nuts on in the safe. That way, no one could get under the car and unbolt the thing.
It is quite strong, someone would have to work hard at this for quite some time before seperating it from the car. Here are some pics: (The white flecks are snowflakes)
This shows it closed up.
This shows it opened.
Hope this helps!
-James