We stayed in Myrtle Beach last week in the mid 90s and kept the rig in the low 70s by running both a/cs. However, with mine being a '12 and only having one factory vent in the bunkroom, I cut the ceiling and installed another in that duct line. I then bought a closeable vent and installed it in the 1/2 bath(and closed it almost off) and it made a huge difference over last year.
2012 Sandpiper 365SAQ weighing @ 15k, Onan, 2nd air, slide toppers, TST
2013 F350 6.7L Lariat 4x4 CC DRW,Viair 1007, Ride-Rites, Edge CTS, B&W
2001 Chevy 3500CC DRW 4x4, 8.1L, 4.10 gears w/ Detroit TrueTrac
2001 Ford Excursion Limited 4x4 7.3L,V/B Spring Mod, ProComps, Hellwig Swaybar, & other 'Necessities'