There is no law in Alabama regulating the seating of passengers in your pickup cargo bed (or flatbed truck). In other words, the state will not prosecute you for carrying passengers in your cargo bed unless your behavior can be characterized as reckless or in violation of a related state law. Keep in mind that even though Alabama does not have restrictions on riding in truck beds, seat belt and child restraint laws may apply to people riding in truck beds. Of course, if an injury occurs involving passengers seated in your truck bed, your insurance may or may not cover it. You may wish to consult your policy before engaging in transporting passengers in a truck bed.
Alabama does not have a law specifically requiring animals to be secured when being transported in the open area of a vehicle. In other words, the animal does not need to be restrained or secured whether inside an enclosed part of the vehicle or within the cargo bed. However laws prohibiting animal cruelty may always be invoked if a police officer determines that a transportation method rises to the standard of cruelty to animals. Both the ASPCA and the American Humane Association recommend restraining dogs when transporting them in pickup truck cargo beds.