One A/C will adequately cool the whole 5er, as long as the outside temp is around 90 degrees or lower. Living in Texas and camping mostly in the warm/hot south, we run both our A/Cs when we stop after a hot day traveling. But after the 5er cools down well in the evening, we turn off the bedroom A/C and likely will not turn it back on during the stay unless outside temps are really hot. The rear 15k ducted A/C keeps it cool even in 90+ degree days. But even if I routinely camped in cooler climates I would still get the second A/C just in case.