I have a new package tray for my 72 Demon.
I don't recall, because it's been awhile, but is there insulation that goes down first..? Also, my new tray doesn't have slots for the retainer clips... What am I missing..?
There is an insulation padding that you can put down. I installed the one in my 70 duster with out it. It sits a little higher on the sides due to no insulation but its barely noticeable.
As far as retainer clips mine didn't have any either, it sat on top of the teeth that held the head liner, and then the window side gets the rear window seal over the top edge. The front of it sits below the rear seat frame so I'm assuming that's all that would be needed to hold it in.