You didn't mention if you were specifically interested in the sport tailbag to clip into the sport saddlebags or not, but if you are you should know that the larger, "regular"
Cortech Tail Bag will also clip into the sport saddlebags (that's the setup I use, though mine is a few years old, don't know of newer models have changed). It has an interior compartment and a pocket on each side also, with a zippered pass-through to make one large compartment. I was able to fit my thermarest pad 20" long in with a little width to spare. If your tent wasn't too big around and no longer than 20" or so it would fit in too.