Never liked transporting spare batteries around in the back of the car, we used to have wood box for the job but that didn't really solve the problem. I looked at the battery boxes sold for boats and camping but decided to use the the battery tray off a junker Rover and bolt in down in the trunk so the most standard sized batteries will sit in it and be safely clamped down.
Pictures aren't very good it started to rain heavy just as I finished
" We're trying to plug a hole in the universe, what are you doing ?. "
(Walter Bishop Fringe TV show)
Pretty smart. Looks better than a whole box taking up trunk space. I killed the back seat of my Chevy Beretta when I was a kid carelessly leaving a battery there. Now I'm much more careful.