I'll chime in here...
I say, ditch the RTT idea all together. I have a JK, and getting my kids up into an RTT in the rack was a pain. In addition, you can't stand in an RTT, and that can be a problem. We were stuck in heavy rain more than a few times, and the RTT was fine for a few hours, but after a while, you want to stand up and stretch. The kids get tired of being stuck inside and not be able to play more liberally. Our RTT took up pretty much the entire Gobi rack, with a small amount of room up front. This wasn't the biggest RTT either, but still meant the rack was almost exclusively the tent.
This was my final solution:
http://www.alphaexpedition.com/oztent-rv-4-5-person/
I actually ended up getting the Oz-tent RV-5, which is a bigger tent than I listed there, but I think the RV-4 is a good size for most. I really wanted a lot of room, so I went with the large tent. This thing uses up only a small amount of space on the side of the rack, and there is plenty of room for tons of extra gear up there. The setup is ridiculously easy, but again, it's Oz-tent, "the 30 second tent." It takes me about 3 minutes to setup. But yes, it's up in about 30 seconds, it'll definitely get you out of the rain or bad weather in that time frame, but if you want the full setup, it takes a little longer to stake it down.
What a difference though. The kids can actually play in this tent, our little one can crawl around and has plenty of space, our daughter who turns 4 soon can play inside, we usually setup a little table in there for them, and my daughter can color or do other things, or they can do puzzles or play with toys on the table. Best of all, we can stand, stretch, move around, and my favorite part.. you can be outside under the awning, it protects you from the weather, and you can setup even more chairs and tables there. They are solidly built tents, strong frame, and thick canvas like what you find on good RTT's. Tons of windows too, if you unzip the rear window, you can actually star at the stars at night while you sleep.
We have a trailer too, but the RTT is pretty much done for. I'm going to be removing the RTT from the trailer soon and getting rid of it. Adding a rack to the lid instead to hold the Oz-tent + extra gear as needed for trips with the trailer. The only real benefit left for the RTT is if we have really foul flooding weather, and the water level rises pretty high. The Oz-tent has a raised floor to prevent this, but if things got really bad, we'd have to relocate. Though, if things got that bad, I'd be planning my exit strategy from there a lot sooner than that I'm sure.