I myself sleep in the back of my truck w/camper shell. Since I am over 6'2" I don't fit w/the gate up, so I made some custom shelters for the back. For trails like the Rubicon where I pack light, I took a small two man 2 pole tent, cut out the back enough that it will slide over the shell and bed of the truck, I had the cut edge sewn with elastic in it to fit snug and keep the bugs out, it only cost me $20 total. For most back country trips I have a stand up shelter that attaches to the canopy and tailgate(the shelter is a modified 54"x54" shower from Cabella's). This modified shelter was a little more at $130, but it makes winter/snow camping in the Sierra's a picnic. I also have a 10'x10' E-Z shelter w/sides for winter camping as well. My buddies and their wives have switched to tent camping, to have more room, and most of their rigs are too modified sleep in(37's makes a rig it hard to crawl in and out of ). They use air mattresses to get up off of the cold ground/snow.

One buddy of mine used to put his 3 man tent in the bed of his truck for snow camping, or when the ground was real wet. I know they make one specifically for that, however the average 3 man tent is only about $60 vs. $150-199 for the truck bed tent, and it is easier to pull out when wanting to wheeling.

One company used to make a free standing tent with a vestibule that attached to SUV's and trucks w/shells, but I am not sure if they are still available.

Here is a trailer site seen one set up at an outdoorsnman expo back in January. Seems kind of cool, if you didn't hit a lot of tight rocky trails with it, and if you could put on at least 31" tires.
http://www.jumpingjacktrailers.com/