If you don't want to make your own, Harbor freight has a few, but DON"T get the kind that go together with bolts! Cabella's carries several and has some good sales. If you are near one of their stores look in the Bargain Cave, always seems to be one or two back there. Thule makes a nice one, but it's pricey!
I really like them for camping and long trips, even if I have the cargo box on top. Stuff I only need to get to when I'm at my destination goes in the Hitch Haul with a big bungee cargo net over it. Cooler and tent and screen house and stove and big box of misc. camping gear and folding chairs and water jug all fit on mine in one big block. After the cargo net I stretch a big ratchet strap or two over the whole mess to keep it from shifting when I leave the pavement. You could put a tarp over the load before the net if you're going to be getting dirty or really wet. I've seen some nice boxes made-up to fit on them, and I've seen those salmon-sized Igloo coolers fill one up too.
One consideration though is dirt... The back of an XJ gets awfly dirt and if you happen to leak anything it'll be all over the stuff you have back there. I'm not saying don't do it; just making sure you take that into consideration before you put the white linens there when you move
I want to get one too, dont have a way to make my own.
