I wanted to make a pattern for the backing plate, so I could be sure it would fit properly before cutting my 18mm stock.
The designer had previously posted a drawing for the backing plate on the CLC PocketShip forum, which I had printed and stored in my build manual for reference when required.
Here is the drawing.
It looked quite straightforward. Here is the scrap ply pattern.
The top edge has been planed to a curve to match the cabin roof cleats. It fitted nicely!