I'm in the design process of a modular trailer. A little different than most, I'm designing a frame that can be used for a variety of purposes. The teardrop portion of it will be a shell that bolts down to the frame, but which can be supported on jacks to allow the frame to be driven out from under it.
The trailer will most likely be made from 2" square tube throughout with eight 2x4 sockets at various points and an aluminum treadplate deck. The axle will be a 3500# with a future option of disc brakes under the 30x9.5" tires on 15x8 wheels. I did some measuring today and the Jeep has a track width of 67.5" from the outside edge of the stock 225/70R15s. When I get my larger wheels and tires, I expect that to increase by about 1.5". The trailer that I've been borrowing is considerably wider, leaving tracks in the sand with a good 2" separation between it's tracks and mine. With that, I'm guessing it has to be somewhere around 20" wider than the Jeep. The trailer I'm designing has a 78" track width, which doesn't seem so bad.
The lateral tubes are 24" on center, making the useful length at 10' 2". The two running lengthwise are 48" on center.
I made the laterals at 24" so that I can order the treadplate in 24" x 48" sections and fit them with as little modification as possible. The outer edges are another story.
The sockets allow me to install a wooden box frame so that when hauling lumber or bricks, I'm not marring something I care about.
For the teardrop, I'm not sure if I'll build it to occupy the full 10' or not. At 5'8", I can sleep sideways and keep some space up front for a cargo box and jerry cans. I probably won't have much of a galley, if I have one at all, although I might change it up a little and put everything in slide-out side compartments. I'm thinking about just having one door on the back and not using side doors at all, making entry more like an APC than a teardrop, but I have time to work that out. The top does need to have a flat spot, or at least flat enough to allow me to attach my safari rack.