I read a post fairly recently about someone replacing the bedroom vent with a 2nd ac unit. The problem is that most standard C units are 30 amp so there's not quite enough power for two full sized units.
I wish they made a small 5,000 btu roof unit for that application.
It would be nice in mine to have just a bit extra capacity...but honestly it's really only needed to cool down an already hot unit, say that's been parked, then trying to cool it down right in the hottest part of the day.....or arriving at a sunny campsite at 3PM on a really hot day.