Instead of using the corrugated slabs (above posts)for seat cushions, I made the cushions and seat backs as strip-and-panel boxes. If I had used the corrugated pieces, I would have had to paper the fluted edges, and I still would have had to clad them with cardboard strips and panels.
The front seat is done, and is dry test-fitted into the interior.
It seems to take as long to do an interior as it does to do an entire exterior.