I decided to finish out the upper and lower body tubes before attaching the fins. So, coupler first, then the ejection baffle.
This is a 6" coupler, with bulkheads in both ends. The forward bulkhead will have a 5/32" eye bolt for attaching a nose cone tether. The aft bulkead will use a heavier 3/16" eye bolt for shock cord attachment, and a reinforcing disk, since this bulkhead will bear the force of ejection.
After securing the eye bolt in the aft bulkhead, I glued a .625" piece of split coupler into the end of the tube for bulkhead reinforcement, then epoxied the bulkhead behind it. After the epoxy had set up, I epoxied the forward bulkhead/eye bolt assembly into the other end, then set everything aside to cure.
The baffle is a standard design—two opposing plates (cut to my specs by Rocketry Works) with holes offset from each other—with the addition of two short tube sections. The smaller diameter tube attaches to the aft plate; the larger tube to the forward plate. This choke/collector setup confines the flow of hot particles from ejection, without restricting the flow of gases.
I attached a 3/16" eye bolt to the forward plate for shock cord attachment, then cut the short tube sections and epoxied them to the plates with J-B Weld.
I let the J-B Weld set up for several hours, then epoxied the forward plate into the tube, behind a .375" reinforcing ring.