I used to ride the ferries when I was sea kayaking on the AK-BC coast and always had a great time. I was young and never booked a cabin just camped out on the comfortable chaise lounges on the covered and heated back deck. I did not have to dress up for meals which is good as all I head with me were my standard trail gear consisting of carharts.
I am looking at taking my wifeto AK on the ferry and will get a room as she likes more creature comforts than I, she will only be with me one way I may skip the room on my solo trip and do the back deck again for the sake of nostalgia, saving the money is not a bad thing either. One nice thing about the back deck is claustrophobia is not an issue, I have spent some time in very small berths in the bowels of ships that were not very comfortable.
