Once when we were returning from a steamboat gathering in BC to Lopez Island via the San Juan ferries, we had to back down a long ramp (75 yards or so) with our boat. The fellow ahead of us was trying to back his car (no trailer) down the the ramp; it took him three tries and almost hitting the railing. I'm pretty used to backing (one does it a lot with boats at launch ramps, of course) so we just rolled down the ramp in one go, an managed to snake the trailer neatly into the cubbyhole they had left for us on the ferry. Phew! Watching people back down is great sport there, so it's nice not to flub it.
The Airstream is definitely harder to load on the ferries than the boat since one has to keep an eye out for overhead obstacles as well, and the visibility just isn't very good.