I believe there were two vehicles plus the trailer in the diagrams. The trailer was not attached to either of the two vehicles, so to me, that would make it a third vehicle. Maybe in police terminology, it’s only a vehicle if it has an engine in it, or something.
But it was certainly a place that should have been searched if they were trying to do a thorough job on the crime scene. Particularly since according to the police accounts, RG was free to move about the crime scene for quite some time before they finally decided to handcuff him.