I think that a double barrier is only potentially bad if the barriers are on opposite sides of the insulation. I don't think there is anything wrong with what you propose. Actually, the drywall can be a vapor barrier if the correct sealants are applied in the right way. Also, there is some debate whether the double barrier on either side of the insul. is actually bad or not. Heck, what about Tennessee where you need heat in the winter and AC in the summer? I'm sure others will have different ideas but I think you are fine. Also, be advised that if your house is super tight that you should probably have an exterior air exchanger, or whatever they are called, to avoid excessive indoor pollutants. These use a heat exchanger when exchanging air to the outside so you don't lose much heat or AC.