There's not much to say except sit back and enjoy the ride.
Did PR to Haines in 2013.
Personally 36 hrs is enough on the ferry, it's not a cruise ship and that leg is he scenic one anyway vs taking it up from Bellingham.
You already know about no access to your camper except when in port. Gas is turned off and bring your sleeping bags or get a berth for the night.
One thing we'd have done if we had the time was de-board the vehicle in some of the towns along the way and spend time exploring the SE coastal areas. An hour walk with the dogs was not enough. I'd assume that would require more difficult scheduling issues especially considering your late start on the reservations.
We booked in Mar for May of the same year and were limited in sailing options.
