Hi Graham @paulinec1

Welcome to the Club.

It is referred to as a Tonneau cover and you’ll see them come up for sale from time to time on ebay (though I’ve just checked and can’t see any there today). They fit over the convertible’s folded down roof and are secured via some wire clips on the outside edge and press-studs on the inner edge.

Sometimes members have them for sale too.

Laurence