Thanks Paul, helpful.
My thinking with the oversize/undersize issue is that If I make the former to match exactly witht he door panels and then add CF the panels will be Xmm to big, as you say, but if I then stick the same CF cloth to the doors then they will also grow by Xmm so be the right size again. Make sense?
This guy makes it look easy :
https://www.youtube.com/watch?v=0Yaggj16S08&t=1195s