Start by cutting off the skin. Now trim off any rib tips (bones) still left.
Place the pork belly with the skin side down and cut lengthwise along the longest edge almost all the way through. Stop when there's 1 inch left. This is so we can open it up like a book.
Now brush the inside with a layer of mustard. Then sprinkle the tarragon and sage on top.
Roll the meat up, roll it tight, from the thin end, and tie it up with butcher's twine.
Apply the rub on all sides.
Fire up the grill, prepare it for indirect heat. Try to keep it at 130° C / 265° F. Place a few chunks of wood on the glowing embers for smoke flavor. Place the porchetta on the grates and close the lid. Smoke it for approximately 3-4 hours, it is done when the meat temp is 95° C / 203° F.
Now bring the meat in, and let it rest for 30 minutes, loosely tented with aluminum foil, before slicing and serving.