More dismantling tonight. I didn't get dirty, though, because I didn't go under the car at all! I think that's a first. Instead, I started ripping out the interior. First to go were the front seats. Surprisingly (to me) the front seats are only held in by 4 little bolts. The bolts were unlike anything I had seen before, kind of like an inverted torx design, but an 8mm socket fit over it well enough to get them out. They were a bit stiff because they're coated with Loctite during installation (I will need to put more on when I put the seats back in) but they came out without too much strain. So did the seats.
Next I tackled the back seat. It was even easier to get those out - no bolts at all - just a couple of push-fittings and then a bit of manipulation. Good thing I have the official manual for this car, as it wasn't obvious at all what to do just by looking at the seat. The rear seat belt attachments were a little trickier, but they were no match for the 600 ftlb air wrench followed by a 2 ft breaker bar! A little bit of sweat and, voila, no seats!
It was too late to take any measurements for the battery box, though. And I'll be traveling for a few days so I won't be able to get back out to the car until next week.