Thanks, Bob. I'm using forward retention only as described earlier in the thread and it will be more than enough for this rocket. In case you want to search for one that will work, the OD of the tube is 3.14". I'm not aware of an off-the-shelf retainer from Aeropack or anyone else for that matter that will work with a MD 3.00" rocket. I know it's been done on some of the smaller Mongeese. But even if there is one that would work for the 3.00" tube, it would have to be 'faired-in' to allow a smooth transition for the airflow over it. There's already going to be an ample supply of heat during boost, and that would increase drag in that region and also create much more heat. This factored into my decision to use forward retention only.
(Sorry, I forgot to add a picture) Here's the business end with the AMW case inserted. I'm going to have some turbulence due to the thrust ring being larger than the OD of the tube. At this point I don't plan on machining the ring , but in time I might change my mind and do just that.