So, if you were run off the road by a road rager, where would that bag (and your gun) end up?
While I'm not necessarily opposed to off-body carry in a vehicle, I firmly believe that off-body carry needs to be secure.
For example, a friend of mine has a secondary glove box under the steering wheel of his Silverado. He puts a J-frame in there while he drives. Push a button, and he has a revolver, but until that button is pushed, the gun is in the box, in an affixed holster.
OTOH, loose in a vehicle = "projectile" in the event of a collision, or even a hard stop.