I took the approach of designing from the ground up as if everything depended on each other. In some small way I feel that this approach should save weight at the end. Where the seams in my floor land on the trailer xmbrs; where the blocks in the floor for the bolts to the trailer also receive the screws from the galley counter face frame legs where they met the floor; where I needed to attach anything to the wall there is suitable blocking placed before skinning (that meant deciding on everything up front: dome lights, coat hooks, light switch locations, pillow light location, wiring paths, etc.), and so on. The more things that can tie together and do double duty, the stronger and lighter the build should be.
For some things it is not such a big deal to go back and redesign or make additions as you go, but for other things it can create very difficult situations to do rework once things have already started to come together. I'm a detail guy and "that's how I roll" and I guess it can be different depending on the style of construction (I am using very thin ply for my inner skin and minimal wall framing, mostly just dedicated blocks glued in wherever anything needs to be attached).
All that being said, it seems that there is no wrong way to build a TD, so long as it does not leak. The most important thing to do is to have fun... and post pics as you go!