If I had to make a carbon tube for a paddle, I would search for carton tube of the same diameter, but with a thin wall for the least amount of weight. Laminate it and leave it there. If you close both ends anyway, the carton doesn't matter.
Don't forget to tape the carton before.

RAIDER-15 (homebuilt)

hey boy, what did you do over there, alone far out at sea?..
"huh....., that's the only place where I'm happy, sir.