Not sure if this is the same stuff, https://www.ebay.co.uk/itm/393779132303 and seems inexpensive.

I used a similar but "quilted" product intended to stop resonance (a slightly different phenomenon), which also comes in sheets and as supplied there is sufficient for lining the boot of small convertibles, so should fit the Mog rear deck.

[Linked Image]

Peter
2009 3-litre Roadster "Ivor", royal ivory / green