Brooks advice in specifications, I used a sheet of fabric to measure out the deck. I managed - just to get both sides of of one 8 x 4 sheet of 3/8" ply. In doing so, I had to shorten the side deck panel by about 1", which will simply mean that the Sapele solid deck will need to come forward by an extra 1" - no issue there.
While I used the manufacturers straight edge, when I cam to laying the two sides on the deck, for some reason which I haven't been able to establish, they did not site together seamlessly, so I had to plane a little off to get a better fit. I don't imagine it will be a problem, as the deck will be covered in Dynel and epoxy, so a gap of 1 mm should get filled up quite easily.
I dry fitted the deck with 8 by 1" bronze screws. I must have used 50 or 60 screws in the process - 2 of which broke in the deck beams, despite setting the torque on th electrc screw driver at a low setting.
Here you can see the deck before it was screwed to the beams and the edges cleaned off with a flush trim router cutter.
Next I moved onto shaping and fitting the side lockers. John Brooks provides a full sized pattern in his plans for one of the locker sides. So I made a template from this and used this to spile an exact copy for all four sides of the lockers. However, this caused some head scratching, as the locker sides are fitted at stations 8 & 10 and these have slightly different hull profiles. This resulted in the locker sides running out of alignment, so I had to do quite a bit of refining. The next picture shows how the aft locker side is higher than the front, which would have cased the seat to run off level, unless lines to the aft bulkhead were checked. Sounds obvious, but anytime I have deviated from John's plans I have subsequently found this to be at my cost...hopefully I have it right this time. Once again a quick email response from John satisfied my doubts.
Next I started to create the V notches in the side locker panel. Based on a suggestion over on the BuildingGlued LapStrake Yahoo groups of using a jig on the router base, I made a simple base with a plastic strip guide. This worked quite well, though with some refinement could be better...ideally longer.
resulting grooves cut into the side panel.