Line a baking sheet with parchment paper and set a cooling rack over it that is at least 1/2 inch off of the surface of the baking sheet.
Pour vegetable oil in a deep stock pot, about 3 inches deep, leaving at least 3-4 inches space to the top of the pan. (The oil level will rise rapidly once the fish is put in it, and it needs room to do so, to avoid boiling over hot oil.)
Heat the oil on medium to medium-high heat or use a thermometer to reach approximately 375 degrees. It should sizzle when flour is sprinkled in, but not smoke.
Cut the fish into 1 inch thick fillets, about 3 inches long. The thick parts of the fish can be cut in half long ways for a thinner fillet.
Pat the fish completely dry with paper towels, leaving no trace of surface moisture. If possible, allow fish to air dry uncovered in the fridge for up to one hour; though this is not required.
Lightly salt and pepper both sides of each fish fillet.
Take the dried fish and dredge in just the rice flour alone (or baking mix), and set aside on a plate.
Whisk together the 1/2 cup rice flour, 1/2 cup all purpose flour and 1 tbsp baking powder in a bowl. (If you are using a gluten free baking mix, this mix replaces these 3 ingredients, so just add 1 cup of mix to a bowl instead of both flours and baking powder.)
Add 1 tsp each of sugar and salt, the 1/4 tsp of garlic powder, onion powder, and paprika, and mix well.
Add the 1 cup of beer/club soda and the 1 tsp of white/white wine vinegar and whisk everything to form a batter.
When oil has reached 375 degrees, or sizzles when a bit of flour hits it, it's ready.
Take the dredged fish fillets and dip into the batter, lightly shaking off the excess.
Carefully drop into the hot oil, it should immediately bubble and fry. Work in batches of 2 to 3 fish fillets, depending on the size so that they aren't crowded in the oil. After 2-3 minutes, flip the fish to get an even color on the other side and fry an additional 1-2 minutes longer.
Use a slotted spoon, or frying strainer to remove the fish from the oil once they are dark golden brown and lay to drain on the cooling rack with plenty of room in between. Repeat with all the fish until it's done. Oil will stay very hot and dangerous until cooled, so make sure to keep the pot of oil in a safe place to cool.