A slide-in truck camper. It's been nearly a year and I still don't have the floor done. Truly an epic lesson in perfectionism, yak shaving, and saving time by starting with the right materials and design. I've learned a ton, but mostly in things I'll never use again. Eh, I shouldn't say that... the amount I've learned about solar power alone I'll probably use in the future to lower electric bills. But nobody really needs to know how to select weather-resistant non-foaming polystyrene-and-polycarbonate-compatible structural adhesives from an SDS, or how to build your own triple-glazed pressure-relief windows, or how to find plywood that doesn't suck. If I knew how taxing and time-consuming this project would be, I would've bought a used camper (and a bigger truck..)