In a large sealable plastic container combine the water, all but 2 tablespoons of the salt and all but 2 tablespoons of the Cajun seasoning. Stir until the sugar is dissolved.
Add the chicken and submerge. Cover and refrigerate 8-24 hours, turning the chicken at least once to make sure all of the pieces get brined evenly.
Fire up your charcoal grill with the Vortex insert full of charcoal.
Whisk together the remaining salt, Cajun seasoning, flour, black pepper and cayenne.
In another large bowl combine the buttermilk and hot sauce.
Working in batches, remove the chicken from the brine and shake off excess. Transfer to the flour mixture and coat well, then shake off any excess.
Transfer to the buttermilk mixture and coat well, then shake off any excess. Once more coat in the flour mixture, shake off excess, then transfer to a wire rack while you coat the remaining pieces.
Transfer to your grill around the now-ashed charcoal-filled Vortex. Close the lid and cook for 45 minutes or until the chicken has reached 165 F as checked in several places.
Lightly brush the tops of the chicken with some oil and cook another 3 minutes to get the skin good and crunchy.
Remove chicken from the grill and let cool slightly before serving.