It depends on the size of the Aspect and your tolerance for higher temps.
I have 24' no slide w/ 15000 BTU. The coach is fairly well insulated, the Ford cab not so much. AC does an adequate job (78-80) in 100 degree weather. If I isolate the cab, it does better. I'm tolerant of temps rising into the low 80s inside as long as there is a breeze (dressed appropriately).
As mentioned shade is a big deal.
If it was a 30' unit w/ slides I doubt the single AC would be adequate for my use. In that case I'd want two roof air units.