Hi Neil, so this method would go something like this:

Planar curve here - build a surface from it using Construct > Planar.



Another planar curve on the interior like this:



Cross sections running in this direction, slightly curved:



Construct > Loft through those to make this type of extended surface:



Trim the loft with the interior curve:



Trim edges with lines to break them:




Select edges and do a Construct > Blend:








That would be a good way to start out I think getting an initial chunk of it done.

- Michael