A lot of passion around this…in my experience I have not had the need to use filler blocks. For my POF models I found that careful shaping of the false bulkhead edges to the required hull curve is critical. Then planking strips will lay smoothly across the bulkheads with the bulkhead glue points being adequate to form a smooth hull curvature. I rarely use filler blocks in the bow or stern as I found that the false bulkhead glue points were adequate to maintain the hull curves. The exception is the blunt bow ships with their very sharp, blunt, bow curve. Still, I use balsa coated with poly with very good results…obviously being aware of the softness of balsa when shaping. Even so, my observation is the primary glue/anchor points for the planking are the false bulkheads rather than the filler blocks. If I find a need I would prefer to build an additional false bulkhead insert glued to the false keel as opposed to a filler block. When I am dry fitting the false bulkheads to the false keel I make note of potential gaps that would need additional support. Then I can trace out a copy of a bulkhead to use to fill a particularly large gap. Just my experience…