Just out of curiosity, why are you using a two-piece commercial ferrule
instead of the simple homebuilt one-piece ferrule in the manual? The whole
idea was to stop spending more money on the ferrule than on the paddle.

A section of fiberglass loom as I use, or a short section of aluminum tubing
from a hardware store costs a couple dollars. Aluminum has the advantage of
offering larger diameters than the fiberglass paddle shaft. This will then
require less shaping of the loom center.

In any event, you won't need to glue the ferrule. Just slide on the
ferrule and wrap a small section of plastic tape around both ends of the
ferrule to loom connection to stop rotation and to waterseal the connection.
It never leaks water, and the ferrule can be easily removed when not in use.

I generally leave one side taped, but remove the ferrule altogether for a smaller packed size when required.

Tom