Great looking cook! As far as ribs getting more tender, what I do is use the toothpick test. At 2 hrs and 30 mins, I pull a rack out and use a toothpick and check the ribs. You want the toothpick to be able to go in the ribs as if it was butter, if when you check the ribs and it is still a bit tough, put them back on.
Then I check every 20 mins or so after that. If the toothpick slides in like butter, then they are done imo. Some will pull and wrap in foil, add liquid of their choice, and use the grate for 20 mins meat side down, I prefer a pull off the bone a bit, I don't like FOTB ribs, but that is just my taste. Another good indicator is pull back on the meat from the bones.
Remember no two racks of ribs will cook the same way, I have had 3 racks cooking at times and one rack definitely done before another one put on at the same time. Enjoy the barrel, I love mine!
-Rob