All three cockpit seat panels have been cut and fitted! The tick stick method works for me and I am now over my trepidation about cutting irregular shaped panels.
One lesson learned: Follow the build sequence (and tips) offered by the designer in the build instructions. John W describes fitting the seats and foreward platform decking before the planks are installed. At the time I was planking, this did not make sense to me. Now, it does. Before the planks are installed, one can cut the seats/decking oversize, run a batten along the frames, draw a line and cut out the shape. I'll do that for my next build.
Next up, the foreward platform panels.