So here I am, closer to the inevitable car door cutting.
Populating the board:
I got a little better as I worked from right to left. I didn't realize how little solder that SMD parts required.
All assembled:
Testing the board:
Everything works perfectly!
Fitting into the box:
The screw holes line up perfectly. The connectors on each end were a bit taller than I had expected, though. The lid still closes, but it pinches the wires a bit. I'll trim a little useless plastic off the top of the connectors and it should be fine.