Here is an idea that might work, or you might think is just stupid...
I looked at your trailer thread, and see that you can weld steel. I had a couple of questions which might impact details, but as a general idea how about this:
Weld a, say 1 1/2", steel round tube frame that fits withins the bed and which provides the rigidity needed for the weight of the RTT when on or off road. To me this would mean tying the four corners together within the bed with flat stock, and almost as high as the bed rail. At the corners at the height you require the tent to be when down for travel install hinges. (The male pipe fittings with a dome shape and a space for flat stock and through bolt, don't have any idea what they're called, but see them all of the time, especially in railings.)
Here two choices:
1. From the joint run the corners up to your required height, ~24" to achieve +6' under the tent. During assembly, make and weld a collar, or buy and install a pre-made bolt on collar under the lower joint, and slide a, say, 2" diameter, about 18" long piece of pipe over the corner post. When traveling you would allow the tent and upper frame to fold forward or rearward as required, when setting up to camp, you would pull the tent and upper frame forward or rearward, as required,allowing the 18" piece of 2" pipe to slid down to the colloar, essentially locking the tent in an upright position. If cross bracing is required it could be installed when the tent is raised and secrued with pins or even bolts, similar to scoffolding. Use the same pins to hold the 2" piece of pipe up at each corner to lower the tent...
Option 2: Since you are looking for a about 24" of rise between the lowered height of the bottom of the tent frame and the raised height of the bottom of the tent frame, put another joint in at ~8" above the first joint. Two joints will allow for less forward or rearward offset when the tent is in the down position. Install the collars on the corner post same as above and the 2" piece of pipe too, but a shorter piece about ~15" long which would slide up the ~16" top piece at each corner. To raise the tent, pull one end and let the 15" piece of 2" pipe slide to the collar to secure the joints. Do the same at the other end. To fold lift and pin the 15" piece of 2" pipe.... Cross brace in the same manner desrcibed above, as required.
I can come up with a lot of reasons this would be a pita, among them the inevitable noise of rattling joints and sleeves, weight... But it would be inexensive to build and relatively easy to raise or take down for one person. A method of keeping the ten and upper frame down would be required, but that might be as easy as a couple of Yakima or rachets straps, some isolation between the upper frame and what it rests on in either option would be good too. Obviously, I have not tried this or even thought long and hard about how to do this, just an idea that came to mind after reading your post.
I'd welcome any thoughts, even "That's the stupidest thing I ever read..." or questions if my explanation was inadequate to be clear.
JPK