I have one of these guys: http://www.amazon.com/Smittybilt-2746-Universal-Secure-Black/dp/B003CGGTUY
The base screws or bolts to the floor. The safe portion takes a quarter turn of the key to release it from the base, and another quarter turn to open. It was pretty easy to hide in my Jeep, and it would take a prybar to get it out.
I've heard that these are good.