What I have done in the past is to not use the decks.
I glue them together and use them as a template and draw the details onto thin 3 ply plywood which can be found in most decent modelshops.
That's probably the best way to use kit 3 piece deck pieces.
For my Revell USS Constitution the gun deck and upper deck are plywood and I have drawn the deck planks using a fine black biro. I cut out the hatch coamings and gratings and use them in the places where they would be if the kit deck was used.
I also did the same with my Heller kit of HMS Victory.