I’m preparing to put the deck on my Southwester Dory. Very Exciting! It feels like a cool turning point.
I did a quick dry fit today just to see if there are any glaring issues prior to joining and 'glassing the deck panels. The parts fell right into place, lining up perfectly with the slots for the bulkheads, and landing right on the cleats and plank edges. WIthout pressing the puzzle tabs together, I did a walk around carefully pressing each panel against the cleats and stringers to get a better idea of how they will lay against the mating surfaces.
The aft panel, when seated on the aft cleat, the stringers, and slotted into the transom leaves a considerable gap to the hull planks. Much too large for a fillet. I also noticed that the aft deck does not sit on the top edge of the #2 plank like the rest of the boat; the aft stringers would have to take quite a bend for that to occur. It seems unlikely that are supposed to bend that far. The cockpit seat stringers easily take a curve fore to aft, but they are several times longer. The only other way to get the aft deck close enough for a fillet would be to bend the deck across the stringers, like an archtop guitar. That seems as unlikely as bending the stringers. Other than the fit against the hull planks, the aft deck panel slides into place perfectly.
Thanks in advance for your thoughts.
After sleeping on it and checking the measurements against the plans (even though I am a kit builder, I purchased the plans to solve an issue I had with the cockpit well sides) I’ve concluded there is only one possibility. Like me in college, the aft deck stringers are a little too high. They’re flush with the cleat at the bulkhead, but perhaps a little better than 1/16" high at the route in the transom. The angle of the stringer hides the discrepancy. I should be able to remedy that. I hope that gets the deck sitting a litte better between the hull sides. It will have to.
Hopefully me talking to myself helps some other Southwester dory builder down the line 
Aaron I am curious how your aft deck fit issue worked out. I am at the same stage with my project. The deck fits well all around except it won’t sit on the #2 plank ledge aft of frame 4. A related question - did you apply a narrow filet on the #2 plank ledge throughout when gluing down the deck? The manual is not clear on that.
My situation was a bit extreme because I inadvertently caused the hull sides to flair more than they should have. I needed to make some cleats for the deck to sit on in the aft compartment; I think I posted about it in a different thread. I then used a combination of weights and strapping to pull the hull in and seat the deck. It was stressful but came out good.
Had I not needed to deal with the flair, I would not glue the deck to the top edge of plank 2. In the areas where cleats were not required I just weighted the deck enough to sit in the plank edge and put the fillet on top. The stringers and designed cleats do most of the work.
I chatted with Jay from CLC during all this and he pointed out the small gaps are not a big deal and that there is even an as-designed slight gap aft of bulkhead 4. I’d say if you can get everything looking good, you should be ok.
Aaron thanks for the reply. My problem was the deck sat a good 3/4 inches above the top of plank 2 (actually plank 3) too much to rely on weight to get it right. My solution was to hand plane the cleats where needed. And added a strip of ash under the cleats to make up for what was planed away on top. Seems to have worked well with decks edges only slightly above the plank edges and close to the hull. Good to hear I can rely just on the top of deck filet to tie the deck to the hull. Thanks again.