it's a given that in certain situation, especially in heat, humidity, AND direct sun, that RV roof air conditioners are not going to be able to 'keep up', at least to some owners...
some 'single roof air' owners will complain that one unit is not enough.
those of us with TWO units will sometimes complain that two is 'not enough'...
there are even those with THREE that might even say the same, at certain times and situations... it's all relative.
Those in tents have a lot to complain about : )