We put dry ice, from an ice house in Bellingham, in the freezer. It worked fine.
I bought two folding, wheeled coolers, for the fridge stuff, there are ice machines.
A lady had some grass cuttings in a plastic bag, a sniff at pee time, got Marley going. It was tough for the dogs on the steel deck. They give you a spray bottle and some paper towels. You can get off at various villages, Sitka and Juneau were our stops, and catch the daily Ferry. Take a tent and air mattress to save the cabin cost. There are also limited cooking facilities, besides the cafeteria, which was good.
We found it to be an excellent trip, fuel savings, just about cover the cost, with no wear and tear on the rig.