Hi,
If you mean under the rear seat squab itself, then I don't believe it ever had anything fitted under there originally, although I'm open to correction on this.
However I've fitted sound deadening material under there.
Best wishes,
Mike.
1954 Series 2: 4 door: "Sally" -- Back on the ground with (slave) wheels, now being sprayed by me, slowly......
1970 Triumph Herald 1200: "Hetty" -- Driven back from Llangollen in Wales (twice.....)
1952 Morris Minor MM highlight with sidevalve engine still fitted, wants work, so joins the queue for now......