Ok, this is an old post, but this is my main concern, too. I had a local welder give me an estimate for a rack an wa going to proceed, but it hit me- what about the gear? It will be exposed to theft, weather, etc. I guess the only option is a shell and the tent on top.
CH,
If you're thinking about the shell and tent on top consider this option...
"Crosstread-Renegade" (this retailer "myladderracks.com" has it for $318.)
It's low profile and adjustable to length and width of any truck, easy to install, has a 750lb capacity, keeps the weight of a RTT and other mounted gear off of the shell, and it's affordable.
With a shell I would also suggest a "Pop&Lock" on the tailgate to lock up the whole cargo area.
I've personally run this set up on two rigs;see attached photos ('00 Tundra w/Maggiolina RTT and '08 Tacoma w/Columbus RTT) and have been very happy with it, although now thinking about an AT Flippac with a growing family in tow.
Hope this info was helpful or sparked some other ideas.
WS