If it is one or two people sleeping inside is very easy and with the XL you have even more room than my Tahoe.
I have thought and researched a lot of RTT's and pretty much decided against one. If you insist on a RTT check out
OVS roof top tent and be sure to look at their 270 awning with the walls. they are both around the same price except the 270 is a lot more versatile and much bigger then a RTT. OVS is also a third of the cost of the REI unit and in many ways better and with a lot more room.
The pros for me of a RTT... Not really anything... Other than a little more headroom in the tent than inside my Tahoe...
Cons they can be very expensive, you can not just jump in the front seat and drive away like I do sleeping inside. If it is raining when I get there I just crawl in back and go to sleep no need to get wet setting something up... Plus after getting wet you have to open it up at home to dry it out.
Inside sleeping is warmer in winter than a RTT and possibly as cool in summer. If windy a RTT is very noisy and drafty.
They kill about 4 to 6 MPG up there and make a top heavy vehicle even more top heavy. Think of bad MPG all the time if you leave it up there or think of the fun on installing or removing a 100 pound plus RTT when you go camping. With my rig from when I decide to go camping to when I am on the road can take as little as 15 minutes packing whatever clothes or supplies I need.
They stress out the roof rack and the stock rack is not strong enough to mount a RTT to it. Remember if the RTT weighs 100 pounds and a couple and gear sleeping in it weigh another 350 pounds you have exceeded the racks load capacity.
In my opinion a ground tent is a better option because if you need to run get something when camping or want to go drive around you leave the tent behind or if you sleep inside you just drive away...
I could give you more ideas and information if I had a better idea of how many people and where you want to camp.
Personally my rig is for somewhat serious off road camping 100 miles out in the wilderness...