After I finished the flashing on the trailer...
I then "lost" all kinds of time on various things that were important but not visually impressive...including a half a day spent moving lumber around to more convenient staging areas (because, of course, the lumber I needed first was on the bottom) and setting up a work area with a tarp for some shelter from the sun.
I spent half a day crawling around under the trailer, finishing the leveling process I'd begun weeks ago when it was too wet and muddy to be crawling around under there. I also took pictures and studied how the trailer is constructed--in order to understand how to install the floor joists so they're on top of the steel supports.
I discovered that some hornets had started to build a nest under the trailer. It was right over my head when I got under there! It took me some time to get rid of the hornets and the nest, but I did not get stung in the process--a major victory!
I won't even try to explain how much time I lost hunting for my tape measure. First it was in my tool belt, then it wasn't. Turns out I managed to lose it on the hillside I climbed to tighten the rope that's supporting my sun shade. Aargh!
Finally, at long last, I started to cut floor joists. These are not screwed down yet, just set in place--but you get the idea.