There are much better uses for teak than something that's going to be in the water all the time, or glassed over anyway. I would worry about pine swelling.
I'd point out again that whatever you end up doing, removing the rudder between trips will help its longevity if that's practical (depends on the pintle/gudgeon design of course)
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)
1984 Fast/Nicholson 345 "FastForward"