I went into the workshop today and talked to Gus about my project, showed him my cardboard prototype and explained what it's about.

He thought that for the concertina bit the best thing would probably be to do something like bookbinding - having 3mm mdf or 2mm pasteboard/illustration board for the slats then cover it all in fabric or canvas like bookbinding - and I should talk to Lee Jensen about bookbinding and how to get the calculations right, etc.