Stan, did you sell those to me in Peterborough, back a number of years?
Big factory conversions have 5 roof airs, because at that price point, I'm not waiting for the coach to cool down if it has been parked in the sun. There is NO EXCUSE for the AC to ever not cool the coach in a noticeable way. No waiting. Excess capacity is part of the price of entry.
Bragging rights to make up for hidden inadequacies might play a part as well...
Riches have their rewards, and their expectations...
In commercial use, think band/entertainer/VIP bus, if there is a failure in a unit, there is redundancy and the coach can continue until it gets the time or to a location convenient for service (or is just left for the next user/owner by the less reputable leasers)
I was told, can't remember the source or the validity, that openings the equivalent of a 4 inch round hole would defeat our busnut efforts at AC, due to the air infiltration issue. Easily that kind of opportunity at the front of the coach, pedals through the floor, defroster, suction around the door is massive, through the electric panels beside the driver, the gap around the old door opening pushbutton on the front, the old air intakes on the sides, and out around every window seal, slider, crack and crevice.
Lots of places blow in by pressure, lots of places suck out by vacuum, due to the coach punching through the air.
Another reason the stock system was sized so large? infiltration, pull down and 39/41/43/47/55/56/57 people all living, breathing and sweating inside. Oh and the driver.... A busnut has only removed the large number of people, the rest of the loads remain.