OK, I have my camera back so here are the promised photos:-
The extra weight of the umbrella has no effect on the ability of the boot-lid to auto open.
The clip kits come with steel baseplates with pre drilled holes so they can be secured through the trim panel with self tapping screws without having to drill into the metalwork of the boot-lid. The clips are spring loaded.
The boot-lid trim panel is so well endowed with securing clips that there is no sag because of the weight of the umbrella.
I used some high density foam which I had lying around and glued it to the back of the baseplates after fitting and before replacing the trim panel in the car to ensure no rattles.
Seems to work perfectly B)
The umbrella, if anybody is interested, is a genuine Jaguar item. As you can see it fits perfectly in terms of length and they are cheap as chips on fleabay.
Yes, the left hand clip looks slightly askew, but my Grandson did that one for me "to make sure I knew how to do it" so I'm happy as it is. Not really noticeable in use :)