they're called 'access covers' in the assembly manual, same in both body styles, the back 2 are to access the wiring for the taillights, no explanation for the others, so they likely have to do with some procedure at the factory
"When we tug a single thing in nature, we find it attached to the rest of the world" ~ John Muir "When we tug a single thing on an old truck, we find it falls off" ~ me Some TF series details & TF heater pics