My understanding from our experience with 2-5th wheels and a travel trailer is that the "ducted" units have the cold air distributed through the camper via hidden ducting between the outer roof and the interior ceiling; the non-ducted just blow from the underside of the a/c and are used in smaller campers.
Our 21' tt was not ducted and worked well because of the small size of the trailer. The same should hold true for the ParkLiner
I would really prefer the roof unit to the under seat one we have if it is not too tall. I modified my storage building's overhead door to 9' so our ParkLiner
would fit into it and can not make it any taller.