I've actually been looking at the same thing and is the only reason I haven't bough a RTT yet, the CC is out and sitting on the desk, just waiting for the dealer to be called so I can swing by and pick it up. Unfortunately, I haven't been able to find a rack that will work and I am thinking I am going to have to go custom to get it done. Although I did like the Thule rack option as it is height adjustable, but I tend to camp a lot alone on my trips as others are not able to get the time off so figured lifting it on the four corners would be a royal pain in the butt.
The reason I want this option is so I can still have a secure cargo area, yes a topper will provide this but I do not want the tent sticking up over the cab of the truck when packed away. The reason I want the secure cargo area is I tend to travel with a lot scuba diving gear (rebreathers, scooters, tanks, etc) in the back of my truck, which is fine for local diving and heading home but on the road which we are a lot and we explore towns, etc, it is nice to be able to leave the truck and not be constantly worrying someone is going to take off with one of my camera's or HID lights by reaching into the bed.
I've been debating doing a hinged model that would lift up and out of the way on either a gas strut or a bar I just installed at the front of the bed so I could easily get access to all my gear. OR maybe just installing a bed slide underneath my existing tonnes cover to give easy access to my gear, hmm and perhaps mount an ARB fridge to it.
Steve