Over the weekend I was able to take closer look. I opened the sunroof and with mirrors and flashlights, I also cannot see the rear drains. Poured a bottle of water in mine and found where the rear drains exit. Appears the rear tubes run down into the C-pillar and drain into the rocker panels. I physically cannot see the tube end. When I crawled under the truck, my bottled water was draining out of the weep holes between the pinch welds on the lower rockers.
I opened the rear doors, pulled down the weatherstripping, and gently pry'd down the headliner. At about the middle of the rear door frame you can see the drain tubes exit the moonroof frame. I too have the safety canopy airbags (which make viewing harder) and was able to follow the drain into the C-pillar. I suspect if you remove the rear seat belts and pull the rear section plastics away you can follow the drains better. I'd try this before dropping the headliner.
Word of caution, the door frame edges are extremely sharp and will easily slice your hands once you've pulled back the rubber door seals.
