What do you mean storage? Get a drysuit and get out there and paddle this winter!

Seriously, I assume this is not an option for you. I'd suggest that you oil the paddle before storing it. The oil coating is not a moisture barrier like varnish or epoxy is, so the wood will equilabrate to the surrounding conditions to some degree. If it hasn't warped or split from usage, I doubt that airborn humidity will cause a problem. I would just avoid putting it where it will get wet.