So the employer or his rep search your car and find a gun. Are they not now in possesion of a stolen firearm? Right to search or not they don't have any right to the property inside, particularly a firearm.
They can't confiscate the firearm unless you choose give it to them because they don't have any legal rights to do so.
If they find it they're not going to take it, they will probably suspend you (send you home immediately) and then call you at home to tell you not to come back to work. Or they might terminate you on the spot. In either situation you'd get to leave with your firearm and never come back.