We got on the ferry in Skagway, off at Haines for a few days. Back on and sailed to Juneau for a few. Then to Sitka for a few days. . . on to Ketchikan and finally to Prince Rupert. Now we did take our small (24') motorhome but there were bigger ones and even semi trailers on board some of the ships. We were measured when we got on in Skagway and got our tickets for the entire trip.
We found the Alaska Marine Highway System to be an extremely professional, helpful, well oiled machine. EVERY person we spoke with on the ferry or on the phone was polite and very knowledgeable about all aspects of the trip. When we got on, they watch the rigs carefully and will block with dunnage boards to help you get on board without scraping. As one guy put it, "We don't want you to break anything either." Considering it could be a black tank. . . hahaha. The guys directing you into your parking place know exactly what to tell you to do, etc. After the first time, we didn't worry about getting on/off again.
This was one of the most pleasurable parts of our trip. The sailings were on time, comfortable, enjoyable, etc.
If you are sailing a long haul, spend the extra dollars for a state room. We did and were able to get some sleep. We also booked one on a shorter run, but it was overnight and that was a good move as well.
Would definitely do it again.
When we got back, I did take time to call them and told them how much we enjoyed this part of the trip and how professional we thought they were and helpful, etc. They seemed to really appreciate it. They seem to be primarily interested in your having a great time in their wonderful state and not having to worry about your vehicle or the journey.
Dale