I can't confirm not having done it but the Classics have Flexsteel and Villa couches and the tour guide at the factory says that everything is brought in an Airstream through the door. It looked as if the couches on end in a line had the back and seat separate from the bases and drawers. Here's a link.
RV Sofas and RV Sofa Beds by Flexsteel
They also had a couch for sale in the office at Jackson Center, how would anyone get it in if they didn't go in finished units?