I went back and found the advice I'd received from Muskrat. It's on this page: https://www.canoetripping.net/threads/gp-build.37137/page-4Jim,
I forgot to ask
Did you do any of your composite copies with the stems closed?
The Sawyer has no tumblehome and slightly laid out stems, I think I don’t need to leave the stems open. Pretty sure it would pop off the plug with fully finished stems.
I also went back and read my build thread where I used a male mold for my composite tandem. I did leave the ends open but when it was time to close the ends I put the composite hull back on the male mold to give it the proper shape. And the dang thing stuck on me after wrapping the ends! I had a heck of a time getting it to release and was legit worried I wouldn't get it without damage. Eventually I did but it was close. I think, because there is no give at all in the rigid stems, that it makes it much harder to break even a light bond. On the main hull a few hits with a palm or rubber mallet will flex the hull and cause separation from the mold but not at the stems.
Alan