update...
car is garaged with the roof off, always.
Managed a 3 hour drive today with a white cloth over the passenger seat without any black spots occurring. I've now left it with the cloth on the seat overnight now.
I have proved one thing however; on the warmest day of the year so far my car doesn't over heat crawling for 45minutes to get through the holiday Llangollen traffic. 1 mile in 45 minutes!
