There is no need to go equipped with foul weather gear ready to go out on one of the Deadliest Catch boats. We were somewhat overdressed having jackets that we use for inshore boating or riding scooters in the rain.
In places like Seward & Valdez the locals are easy to pick out. They are the ones stomping around in the brown or yellow rubber boots. Not needed by us visitors.
A lightweight waterproof jacket to wear over whatever is enough. Most likely something that everyone already has.