Have a look at a previous thread I put in:
https://forum.mx5oc.co.uk/t/fitting-a-centre-brake-light-to-luggage-rack-on-prht/108778
I have used a NB boot luggage rack and fits perfectly and attaches itself via four allen keys that tighten rubberised clamps to the underside of the bootlid.
However, if you have the hard top, make sure you place the first clamp away from the rear of the bootlid 175mm away, otherwise you PRHT will clash with the rack.
Hope thas useful
Russ