Air conditioning or any kind of forced air heating/cooling typically dries the air out. If "South East" is somewhere like say cajun swamp country then from what I hear RH in the 80's could be normal. If you've got another meter around might check in the room outside the tent to see what the RH in the room is. If you're in a really, really high humidity area to begin with could think about a dehumidifier. Small bonus with that of getting some nice "distilled" water to use for the plants from emptying tank(s).