You might as well just leave the gun on the front seat. Get the safe secured permanently, prefer in the trunk where hidden from casual walk by observasion. Remember also that if your car gets stolen you are also loseing your gun. So add some additional trigger deterrant/lock if possible.
I have one that has a cable that is under the front seat. I only store my pistol when I can't carry it with me. (Not very often.) I have another one that I screwed down in the trunk of my wifes car. Neither are impossible to get into, but it would make a heck of a racket! Both safes double to hold extra cash while traveling.