The stock pannier rail with bag are what I ended up going with. I got one for each side. Doesn't have anything to do with the shorter fender, i don't think. It attaches to the frame. The only issue with them is that they come in Chrome only. So, I had mine powder coated black before install. I installed myself with the help of a friend. You can do it with no small difficulties without removing the mufflers as is stated in the instructions. It's a pain, but as long as you're careful, it's possible. I'm happy with mine. The bags have pretty decent capacity and when they aren't on the bike, the rails don't look out of place at all, imo.
Pannier Rail part is A9518218 for the left side and the bag (in black) is A9518230. 13.8 litres of capacity. If you have a Triumph dealer nearby, I'm sure they will have them on display.