When it describes the installation of the seatback stringers and the seatback panels the manual advises us to very carefully drill pilot holes in the 9mm seatback supports and to use skinny temporary screws to hold everything in place.
The chance of something breaking or kinking seems high, and it would be a really fussy thing to do when the simple addition of cleats would solve the problem.
So I made cleats from scrap ply and glued them in place on each seatback support, like this.
Here is the starboard side, suitably reinforced.
We now have plenty of material to fasten the stringers and panels with temporary screws without worrying about breaking a support or a stringer.
Not terribly pretty, but perfectly functional and never to be seen again when the seatbacks are sealed up!