Hi Andy,
I did not have any original trim in my car, so after some considerable investigation I discovered:
The up stand behind the seats that you are referring to was covered on the front face with vinyl and under this was a thin (1/8" ish) Jute material. I found the alternative scrim foam too thick and spongy at about 3mm, so I chose to use an old woollen short pile blanket that I was given by my mother in law!
I cannot be conclusive but I believe the back of this panel is just painted satin black.
I chose to cover it with vinyl but no backing.
The front boot board over the IRS slides under the bracket at the front of the IRS hump where the hinges are and at the back there is a bracket
https://www.sngbarratt.com/uk/#!/Englis ... 90ab782ab2
(that's expensive!) screwed on to the bottom of the board and three screws go through this and into some raised "top hat" brackets spot welded to the rear of the IRS panel in front of the tank.
I can post some pictures if you need them.
Regards,
Paul