Well, the first major step in my journey is complete: I purchased a trailer. I ended up buying an old enclosed cargo trailer, which I am in the process of demolishing down to the frame. (I hope to reuse, recycle, sell, or give away most of the materials composing the enclosure.) I found the trailer on Craigslist and bought it for $900. Unfortunately while driving it home (from Pullman), I lost a wheel. I didn't even notice until a lady pulled up next to me and rolled down her window. "You lost your tire!" she shouted. "What? It popped?" "No, it fell off!"
The bed is 18'x8', which is the small end of the range I was considering. As such, the design will be trickier - and in some ways more fun. But I've scrapped the "attached two-bicycle garage" idea I fantasized about when looking at longer trailers.
Most tiny houses like mine feature a "cathedral ceiling" in the living room area, with the kitchen and bathroom under a loft. At first I planned to do the same, but now I've decided to reverse the typical layout, placing my living room under a loft and my kitchen under the vaulted ceiling. It just makes sense to me that in the living room where most activities involve sitting, a high ceiling doesn't matter near as much as it does in the kitchen, where you stand. Besides, from an ideological perspective I like the kitchen as the nexus of the house, the place in which people naturally gather - it's reflective of a healthy household economy.
So, the front 7 feet or so of the house will be the living room, with a 6'4"ish ceiling and sleeping loft above. The next 7 or so feet will be the kitchen, under the open ceiling, and another three feet will be the bathroom, with a low ceiling again and storage loft above. The kitchen will have counters on one side, and on the other a fridge and desk/table. The living room will feature a built-in bench/couch/guest bed with storage beneath. For board games or formal dining, the table from the kitchen can be moved in front of the bench.
Anyway, the next steps are finishing the demolition, purchasing my windows (probably on Saturday) and after those tasks are complete, creating construction plans. When I go to the tiny house workshop in Chicago on September 15-16, I want pretty detailed plans so I can get thorough feedback.