: The seam/tape would probably show up on that nice polished deck.

Hi John,
It wouldn't show if the 'seam tape' was the full width of the deck on the outside.
The best reason to make a hull and deck seperate and joining them at the gunwale/sheer is symmetry/fairness. It's easier to see any anomalies in a hull if both sides are one piece.
If you really know your molds and parts are going to be symmetrical/fair, there little to stop you from doing a centreline seam.

Mike Savage
South West Cork