If you can contact Ruger, they will be able to tell you straight from the horse's mouth how the stock will stand up.
Generally, laminated stocks will hold up better than regular wood under harsh conditions. Not as good as synthetics, though. However, I have seen stocks that have delaminated (both on Marlin Model 60's).
All this being said, once you talk to Ruger, if you still have some concerns, then you might look into giving the stock a coat of a marine-grade epoxy finish. This should make the stock very durable to moisture, especially if you remember to coat the barrel channel, inletting, and under the buttplate.