Behind back seat?

I removed my backseat today out of my 65 Dart seat no issues. is there supposed to be some kind of backing that is between the backseat back cushion and the metal frame? If so what should I use? any pictures?

Thank you

They are made from Masonite, you can make them from any medium/high density fibre board (what I did), although I'm pretty sure Classic Industries sell these and rear parcel trays and the insulation as well (as per Reply #2 above)...