Steve,
The various replicas are slightly different, but generally, fold each side up and over the roof so the width is narrow than the roof bars, then wrap the roof around the two bars.
The Classic Roadsters Ltd. Duchess manual has specific instructions for their car. The manual is in the library. Scroll down to the 25th page of this PDF:
https://tdreplica.com/wp-content/uploads/Classic-Roadsters-VW-Duchess-Part-4-Body-and-Interior.pdf
Paul Mossberg
Former Owner of a 1981 Classic Roadsters Ltd. Duchess (VW)
2005 Intermeccanica Roadster
If you own a TDr and are not in the Registry, please go to https://tdreplica.com/forums/topic/mg-td-replica-registry/ and register (you need to copy and paste the link)