I made crispy pork belly (siu yuk) and after many attempts this has been the most consistent one.
I have used lots of different methods, I used vinegar and salt and leave uncovered in the fridge for a few days and you must wait until the skin is really hard and dry. I did poke holes in it too. For the marinade, just some 5 spice, salt and sugar. Then you place on some foil, and wrap the pork up but leave the top uncovered, this prevents the sides from burning and keeps pork really succulent. I put in the oven 40-60 mins at low temperature 100 Celsius to dry out the skin even more, then turn up to max for 30mins (watch it doesn't burn), then turn it down to 180 for another 30mins.
Thanks