As a condition of bringing your car onto his property, he can require you to submit to a search of the vehicle. You are, of course, free to refuse and seek employment elsewhere.
Also, I have a Right to carry my firearm while in my car to and from work. Giving my employer the legal authority to ban my gun from my car strips me of the ability to effectively provide for my own defense while commuting.
Private citizens have no duty to help you exercise your rights. Your ability to defend yourself going to and from work is not your employer's concern.
Allowing me to keep my gun in my car in no way infringes on the employers equal rights of property in their ownership of the parking lot or buildings.
You have every right to keep your gun in your car. However, you have no right to use your employer's parking lot in violation of his rules.
In a publicly accessible parking lot? No. Not without a warrent they cannot. I'd hold a different opinion if they were gating it and had armed security.
Private citizens have no duty to help you exercise your rights. Your ability to defend yourself going to and from work is not your employer's concern.
Nor can private citizen arbitrarily strip another of their Rights. No help is required.
You have every right to keep your gun in your car. However, you have no right to use your employer's parking lot in violation of his rules.
If they have the parking lot open to the public, then they also have to respect the equal Rights of those individuals that will come along with it. Just because my car is on their property does not give them de facto ownership of said car.