Do it the other way around and use Super Glue. I tried the "glue the ball on top" method and I thought it worked really well:
https://www.muzzleloadingforum.com/...did-you-do-today.134755/page-762#post-2662956
You close the powder cylinder off with the flaps at the top before you glue the ball.
You don't need spray starch to stiffen your powder cylinder, you just need heavier paper. I found that curling paper works the best. It's heavier than cigarette paper, makes a sturdy powder cylinder, but not so heavy that the percussion cap flame doesn't penetrate.