That said, any employer who would object to an employee having a gun is a moron.
I must disagree. I contend that this is a primarily a property rights issue being used as a wedge to restrict the RTKBA. Specifically, I maintain that an employer's property rights do not overrule an individual's "castle" rights.
A vehicle is an extension of an individual's home and castle. What is in it is nobody's business except the "king of the castle". Additionally, the Second Amendment is an individual right. Therefore, the employer has absolutely no say over what an employee has in his vehicle. And that is especially true when it comes to "arms" and the right to keep and bear arms.
What the employer does legitimately control is access to his property. He may deny or permit access to parking lots, grounds, and facilities to units, i.e. people, vehicles, etc. This denial can be based on a broad range of criteria but stops short of interfering with an individual exercising his Second Amendment Right in his "castle" (vehicle).
An employer may allow or restrict the individual's "castle" (vehicle) access to his property. But the employer has no access to nor control of what is in that "castle".
Basically, within his "castle", be it home or vehicle, the individual answers only to God and the law, not to an employer. Remember, our founding fathers did not create the Constitution to ensure freedom from risk but to define risks to ensure freedom.