I know of no law regarding the carriage of rifles and shotguns in your car. If you have a pistol in your car, have a license. Some will carry it unloaded in their trunk, but Alabama law is silent on this practice. If comes from federal law regarding transporting your firearm interstate from one place where you are allowed to possess it to another. The federal law specifically mentions interstate and does not mention intrastate.
Even if a court would rule that unloaded carry in your trunk is lawful, a LEO seeing you put your gun in your trunk and drive off might stop you and ask for your CPL, arresting you if you don't have one. The law is vague enough that, even after you are acquitted, you won't necessarily have recourse against the officer, so they would be able to keep stopping folks for unloaded carry in the trunk without a license.
Anyway, for a better discussion on this, visit http://AlabamaOpenCarry.com/forum. That's where most of the open carriers in Alabama post.