Your briefcase is your personal property, and an extension of your personal property as is your car, would you then consider taking a loaded gun into your workplace in your locked briefcase?
You have no right to bring the weapon into the property owner's space regardless of whether you bring it in concealed (in your car, your briefcase, or your trousers) or openly. The property owner's rights allows him to set the rules for the access, use, and stay by anyone on his property, and the rule is that no guns are allowed in the space that makes up his property. The gun is in your car, and your car is on his property, which means that the gun is on his property, and that means that you have violated his rules for access and use.
You can be fired for having a loaded weapon in your car if you park your car on his property.
Yes, you are correct, I am violating a work rule and I could be fired if caught. I would be breaking the law if I carried concealed through the main gate since it is posted but I am only breaking a rule by having my gun in my vehicle.
I am not worried about losing my job, good jobs are easy to find in my field, but I am worried about losing my life, that's why I ignore this work rule. What the company doesn't know won't hurt them or me.
I'm hoping our gun rights group, GrassRoots South Carolina, can convice our representatives to pass a law like Oklahoma's.