We 4wheel, explore and now overland in a 2005 Jeep Rubicon LJ. We have 4" more space than a regular TJ. I did install the Smittybilt lockable drawer for the JK (which actually fits the LJ nicely let me know if you need a pic and specs on this). We took the back seat out to accommodate the drawer. Our kids are out of the house, so that space went to my service dog.
Our jeep has a Garvin Wilderness Rack on it for cargo. It is lifted with a 3" Rubicon Express lift and I run 33" Duratracs. With that said, with the racking it makes it roomy on the inside, but everything is on the roof and gas mileage suffers all the more. But it's a Jeep thing and others just don't get it, you can't beat the ride....at least in ours.
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As a result we bought a Kakadu Bushranger 200XT trailer from Kakadu Camping in Delta BC.
The Jeep is more than capable to tow it, and gets a lot of the stuff we had on the roof off the jeep into the trailer.
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Most of the stuff came off the roof. We ended up leaving the tent camping stuff for non-trailer camping on the roof and won't take that with us when we take the trailer.
Now that I have the trailer and have used it camping and travelling from BC to Ontario camping all the way, I do not believe we will be overlanding without the trailer anymore. At least as long as we have the jeep.
As for putting at RTT on the TJ, dude it will affect your ride adversely I think. This thing has the aerodynamics and handling characteristics of a garbage dumpster, it will put you really high centre and tippy.
In my opinion dude, go with the trailer with a RTT that has the same width or smaller than your TJ so that where ever you go it will go.
Hope that helps.