Top boots are common to convertibles. Every manufacturer that I know of offered them if they were not included with the car. Until you posted the photo of Bob's car had I never seen one on a Speedster. Seems like a fitted boot would be common and not the useless half tonneau.
I never liked it
$2700 replacement cost.
When I found out, I called OK Foreign and told them I’d buy every one they had. They laughed. “It’s the first thing that goes on a Cabriolet.”
Works just like the one Jim made, only a 968 has two access doors to the trunk on the parcel shelf (that replaces the “rear seats” because Cabs don’t have a C pillar for a shoulder belt anchor) The boot tucks behind those doors and they shut over it.