Matt with Sovereign Arms LLC here . There is not a law prohibiting you from carrying the firearm in a commercial vehicle providing you are legally able to posses the firearm. The restriction however would be (legally) that every business or company that is privately owned can set it's own rules inregard to employees bringing firearms onto their property. The employees are subject to the employee rules set forth by the owners of the business and if employees violate those rules they could be subject to termination. I had a student in my class last weekend who drives for an automotive dealership and delivers parts. He was asking the same question you are. If you have a concealed carry permit and you chose to carry when you are working it should fall under the section of revised MO statute 571.107:
(15) Any private property whose owner has posted the premises as being off-limits to concealed firearms by means of one or more signs displayed in a conspicuous place of a minimum size of eleven inches by fourteen inches with the writing thereon in letters of not less than one inch. The owner, business or commercial lessee, manager of a private business enterprise, or any other organization, entity, or person may prohibit persons holding a concealed carry endorsement from carrying concealed firearms on the premises and may prohibit employees, not authorized by the employer, holding a concealed carry endorsement from carrying concealed firearms on the property of the employer. If the building or the premises are open to the public, the employer of the business enterprise shall post signs on or about the premises if carrying a concealed firearm is prohibited. Possession of a firearm in a vehicle on the premises shall not be a criminal offense so long as the firearm is not removed from the vehicle or brandished while the vehicle is on the premises. An employer may prohibit employees or other persons holding a concealed carry endorsement from carrying a concealed firearm in vehicles owned by the employer;
It is not illegal according to 571 to have a concealed firearm on your person ; on private property(even if it is a public venue and posted no firearms) according to the following portion of 2. Carrying of a concealed firearm in a location specified in subdivisions (1) to (17) of subsection 1 of this section by any individual who holds a concealed carry endorsement issued pursuant to sections 571.101 to 571.121 shall not be a criminal act but may subject the person to denial to the premises or removal from the premises. If such person refuses to leave the premises and a peace officer is summoned, such person may be issued a citation for an amount not to exceed one hundred dollars for the first offense. If a second citation for a similar violation occurs within a six-month period, such person shall be fined an amount not to exceed two hundred dollars and his or her endorsement to carry concealed firearms shall be suspended for a period of one year. If a third citation for a similar violation is issued within one year of the first citation, such person shall be fined an amount not to exceed five hundred dollars and shall have his or her concealed carry endorsement revoked and such person shall not be eligible for a concealed carry endorsement for a period of three years. Upon conviction of charges arising from a citation issued pursuant to this subsection, the court shall notify the sheriff of the county which issued the certificate of qualification for a concealed carry endorsement and the department of revenue. The sheriff shall suspend or revoke the certificate of qualification for a concealed carry endorsement and the department of revenue shall issue a notice of such suspension or revocation of the concealed carry endorsement and take action to remove the concealed carry endorsement from the individual's driving record. The director of revenue shall notify the licensee that he or she must apply for a new license pursuant to chapter 302, RSMo, which does not contain such endorsement. A concealed carry endorsement suspension pursuant to sections 571.101 to 571.121 shall be reinstated at the time of the renewal of his or her driver's license. The notice issued by the department of revenue shall be mailed to the last known address shown on the individual's driving record. The notice is deemed received three days after mailing.