Whenever I roast a pork loin, this is the technique I use to make pork crackling while the pork is resting. The key is to score the thick layer of fat on top, then slice it off in one piece, then set it back on top of the pork loin while it's cooking. While the pork rests, if you need to crisp the skin even more - crank up the oven and cook for a further 10 minutes or until it's crispy.
You can make a nice gravy with the pan juices, some redcurrant jelly, stock and a tablespoon of flour to thicken.
It took me ages to get crackling right but I finally worked out that it has a lot to do with moisture in the skin. I have posted an article on http://www.wowbbq.co.uk/Articles/The-Perfect-Pork-Joint-On-A-Weber-BBQ.html here which may help: Although it is on a weber bbq it can be applied to a convection oven as well. Hope it helps. Bring back the Crackling! - 20 Apr 2012
I do 240 degrees top oven for 25 min then 190 degrees 30-35 min per pound in the middle oven always get fab crackling and not dry meat - 15 Sep 2013