Bill, I can see the law overriding all local ordinances for carrying in public places (with exceptions) but don't see how SB292 applies to a police department carrying out their official duties. Riding in a police vehicle with an officer on duty would seem to be something completely outside the scope of 292.
As a police officer, he's a representative of his employer, a local government. The LG is allowed to make rules as to what the officers carry on duty. They are not allowed to have a rule, policy, ordinance, etc. controlling a citizen's ownership, possession, or carry of a firearm more strict than state law.
There is no state law that says a citizen cannot carry a firearm in a police vehicle.
As I said, I'm no lawyer, but I think I'm reading this correctly. Nonetheless, I'm certainly willing to admit error if I'm mistaken.
ETA: Of course, this would not protect the citizen from the "trafficking with an inmate" charge should the officer take him/her into a place where prisoners are incarcerated, though I could see a good attorney finding a way around that as well.
Blessings,
Bill