IF you're going to keep it in a 'steering column' holster while driving, just make sure you take it with you when exiting the vehicle 'even for a minute'. JMO.
'Cause if I'm a bad guy, and walk by and notice that gun hanging under the steering wheel, that's gonna be 'my' gun. Locked vehicle or not, unless those windows are shatter-proof. And if you're coming out to reclaim it, you're gonna have a problem, 'cause I now have YOUR gun pointed at YOU, even if you're coming up on me armed with a second (or backup) gun.
True INGO fact, when HoughMade was in the service his platoon Sgt. made him tape an M60 to his forehead just so he had his hands free to carry a base plate.