Two roof units work better than the basement air but 2 of them is cheaper. At that time they might have been using up in stock stuff. On my basement unit I have replaced 2 squirrel cages, 1 blower motor, 2 pillow block bearings. My unit still needed a roof air for a kicker. For what it is worth. All in all National built one heck of a coach.
Tom Homestead Fl.
2017 Tiffen Pheaton