I've seen many different set ups, not all of them are crammed into a closet floor to ceiling. As long as there is enough exposed duct to slide it in, or whether it be a 24"-30"-36"-42" etc... Long Section of trunk. Its nothing for a tin knocker , even with small access.
Sprinter, he said he lived in a mobile home, I have never seen any exposed ducts in a mobile home besides the cross over tube.
All of the duct work is ran inside of the plastic lined insulation that covers the under side of the home.
For example when u look under there u see nothing but black plastic and one 12-15" crossover duct
To even see the duct that comes from below fan you have to cut out a big section of plastic and then start pulling out all the fiberglass insulation, it's a mess
Also in all mobile homes I've seen, all of them were installed in closets where they simply studded the walls against the unit itself to save room, maybe you've seen something different but out of all I've seen, they were all like this