The reason for not taking a travel trailer on the ferry system is cost. The biggest reason for wanting a truck camper is access to triple the camp sites here in Alaska though.
We are still considering keeping the travel trailer for some camping. But I have never seen any of our national parks (except Denali) and dream of it. We would likely take the ferry once so that I can see more of the lower part of our great state. Storing a camper in the lower 48 for months at a time isn't in the mix. We LIVE here and don' intend to become snowbirds.