You are going to need protection from more than moisture or humidity. Your scope
also needs to be protected from impact and vibration.
I would pack one in nothing less than a hard waterproof case. I am particular to Pelican Cases for this. You won't have any problems transporting it ashore in a wet dinghy
ashore or worry about it being dropped or banged against something. Additionally, the scope will probably last longer in a marine environment
being stored in one of these cases as well. Yes they are expensive, but so is a really nice scope.
I have scientists and engineers who bring sensitive electronics
and instruments aboard in these cases all the time. Quite often the case itself is the enclosure for the controller part of the instrument.