69 barracuda rear seat-trunk finish and tail panel

Pictures would help of your cargo area, what you have and what is missing. Sounds like you have a FB. The basic components are: large rectangular floor, two large side panels covering the wheel wells, five trim pieces under the back glass and down the side of the seats. All cars had the cutout for the defroster but few of them actually had one. The rear door is made of plywood trimmed with three metal pieces with a long hinge on the bottom side. This rear door was commonly carpeted on the inside. If you have the defroster option, it plugs into the wire loom running under that floor near the wheel well.