I will be camping out of mine next weekend for a week, on an Elk hunt. I should have time to take some pictures. I did not really take a ton of pictures during the build, as it took so darn long. I did find one during the build, let me see if it will post correctly:
I was showing my led lighting. You can see the bed down (with my big knucklehead), my front shelf, my rolling battery box and my solar stuff at the far front right. The rolling battery box allows me to roll it over the axle for transport, anchored to the e-track. And I can partially roll it out once camping, as a spare seat for the shelf. This was early in the build.
Derek,
I pull mine with a 2002 Avalanche, very close to what may be your tow vehicle. As I live in the mountains, the big item I need to add to my vehicle is a trans cooler. Otherwise the Chevy pulls it just fine. I have an offroad trailer of sorts for ugly trails, but still wanted "reasonable" offroad capability with my cargo conversion. When I looked at trailers, the difference between a 10' or 12' length looked obvious as to degraded capabilities. But, if really only running forest service fire roads, the added length would be very helpful. They both seemed huge when standing in them at the dealership, but once constructing, the space goes fast.
I wanted mine to not be a fancy RV type, but fully able to be a cargo trailer when I wanted. hence the reason for everything being fold down. I do have a permanent shelf in the front, but it does not really impact cargo ability. I did not go fancy inside, but tried to do everything of reasonable build quality. My CT has a 3500# drop axle, but I did put some spare 33x9.5" BFG offroad tires and wheels on it. Those help get it up, and I can go to a straight axle and pick up another 4 inches if I decide I need it. But one thing about lift, is the door threshold gets kinda high. I am using a full size spare, and have a board bolted to one side to use as a step. 2 for one, as I am hauling the spare anyway. A ramp would make the in and out easier, but then you need 6 or so feet to the length of the trailer for parking and deployment, so opted for double doors.
Mopar posted a cool picture of his RTT on his, and you can get a feel for just how high his is. I would think it great for better roads, but once I get offroad here in the rocky mountains, and I leave the main FS hauls, trees and branches up high can get to be pretty tight. The RTT would be great for the kids, as what youngun' doesn't want to hang out in a tree house? then the double bed couch for you and the Mrs. Other than the headache of putting things out at night, and away in the morning, the RTT would really bring a lot of flexibility to your build.
I keep all of my cooking/camping gear in waterproofish tubs. They all go outside. My fold down bed stays down when camping, to provide seats for hanging out inside. I think the big downside to a couch bed would be losing the storage under it. It would be a ton more comfortable, but space is the premium with these builds. I think you could make a 6x10 (or 12) reasonable for hanging out on the inside during weather, but an extended weather condition would get to be pretty "crowded". Here in the rockies, we get a lot of daily rain during the summer. It blows in quick, and usually has a lot of wind with it. Outside even under an awning can be wet. So hiding from the rain is usually only a few hours. If your prevailing rains are more vertical (and not blowing), a good awning would still allow for outside living. I would give consideration to your typical weather patterns. I used sail/awning track on both side of my trailer, and the tracks is 9.5 feet in length. When I sewed the awing track to the fabric, I made a break at 5 feet. this lets me fold the awning into a reasonable size for transport, but allows me to only thread 5 feet into the track, and the other 5 hangs down. A sort of wall, If I need it.
Your idea of sketching is solid. I would maybe add a length of rope in the yard mocking the pattern. Have the tribe join you in the pattern, and see what you think. As to height, I would say 3-4 inches above the tallest head if possible. I am 6', and have a 6'3" inside height. Mine is not insulated, and I rally do not feel like I have to squat inside. Might be a little snugger with insulation, but if this upcoming hunting trip goes OK with my buddy heater in the evening and mornings, I may not insulate. But I do manage to bonk my head a few times on the door jambs. Never an issue stepping in, but stepping out, I need to get in the habit of screwing my cap on backwards when inside.
I think a 6x10 or 12 would be completely doable for you, if you do not want all the RV goodies like sink, toilet, kitchen etc, inside, with 5 folks. It takes me about an hour to an hour and a half to deploy/pack when not hurrying, but with the 4 helpers you have, I bet you could shorten that ;^)
Craig