Thanks for all the input guys! My understanding is that because it will be on a trailer, and therefore movable - basically like a 5th wheel - that it's not a permanent structure and should get around a lot of the legal issues. I'm googling to find out more about landlording information, but most of it seems to be angled toward tenant rights and not so much from the landlording perspective.
I appreciate the tumbleweed house vs a travel trailer/rv because of it's style, aesthetic, and build quality. I think that this is something that will keep it's value better than an aged out fifth wheel. Plus, I get to gain the building experience associated with putting this together and the comfort of a back up in case all truly goes to hell with my family.
Also, I think I am in a good area (South Puget Sound - outside of Seattle) for this kind of thing. People here tend to appreciate and lean toward the ideals associated with something like this. We're not quite Portland (hehe), but it works.
My thinking was also that with such a small space, and the quality of the materials (no standard walls to be damaged, no carpet, ect) that damaging could be limited, but you never know, people can be creative!