Curious-- what would be the purpose of a gun safe in a car?
With car break-ins and thefts common, police routinely advise against storing a gun in your car. And if you're in the car, ihe gun is no use to you if it's locked and inaccessible.
It's very common for people to not be able to carry their gun in GFZ's like work and still want to have their handgun to and from and anywhere they might go on the way home. GFZ's create most of the need to leave your gun in a vehicle.
Like you, I would never just keep a gun in a vehicle all the time. In the case of GFZ's the added security of a good quality handgun safe bolted down will be much better than a locked car as we know that's very easy to break in.
Be weary of those small thin steel clamshell type cabled lock boxes if this is something you do regularly. They won't slow anyone down from getting your gun, but are probably OK for the occasional brief trip to the post office, etc.