Blanch the pork belly in boiling water for 1 minute. Remove and rinse under cold water. Dry thoroughly with paper towels.
Using a pointed object such as a nail or dart, poke many small holes in the pork skin, pressing deep enough to reach the fat layer beneath. Wipe away excess oil and brush rice vinegar over the skin.
Mix salt and rice vinegar to make a marinade. Coat the meat with this marinade, keeping it away from the skin. Refrigerate for at least 12 hours.
Preheat the oven to 200°C (392°F) with top and bottom heat. Place the pork skin-side up on a large piece of aluminum foil. Carefully fold the foil around the meat without covering the skin.
Cover the pork skin with a thick layer of coarse salt and press lightly. Roast for 45 minutes.
Remove the salt crust and foil. Return the pork to the oven for another 15 minutes until the skin blisters and becomes crispy.