So, what do you expect from your rig AC? We have a 13k BTU AC in the front/master and a 15k BTU in the living. At present, the main 15k AC is keeping the rig at 10-12 degrees lower than the outside...
Our Grand Design 303 RLS in direct heat without humidity will keep about 20* to 25* difference from outside temp with shade and tinted windows insulated with foil bubble stuff. In direct sunlight max difference at about 20*. I am not an a/c expert but my a/c guy at home said you can loose about 30% to 40% cooling efficiency with high humidity cause a/c has to de-humidify also. Worse scenario, go to the pool, shopping or a movie during the hot part of the day! ! ! Good Luck & Be Safe ! ! !