I have also contemplated the same thing. I thought about mounting just below the dash in the middle of the truck (right handed) for vehicle concealment/security and also having quick access. Keeping the pistol concealed on my belt while seated in the truck does make it difficult to access quickly if needed.
There are some youtube videos out showing how easy it is to pop open those flat "safes" with the cable.
I don't have the one in the video, but I did buy a safe to put under the back seat in the pickup. I had to drill some holes to bolt it in, but it works great. The only drawback is that it doesn't allow very quick access.
A neighbor installed one in a center console (which I don't have) and it's was both convenient and secure. Again, it was one that required drilling some holes.