I have the same thing on my #raspberrypi. I tried listing it in /etc/crypttab, but then the boot hung, apparently because I was supposed to input the password but there was no prompt for it. Getting it to boot again was tricky.
Do you have a good idea of how to mount the hard drive when booting?
@rotawerx By any chance are you writing a guide on this? I've tried to do this before with two approaches but I couldn't.
One was using a blank Raspbian an install everything on top but for some reason it was kinda messy.
The second one was modifying the Kodi, which also didn't work too well. #¯\_(ツ)_/¯