installer fails to install grub with encrypted root fs

[Echo Nolan]

I tried to install Ubuntu on my laptop. The system has Windows 8 installed and I'm replacing Nix with Ubuntu. I used an encrypted root filesystem. Not sure which, if any, of these causes the problem.

ProblemType: Bug
DistroRelease: Ubuntu 15.10
Package: ubiquity 2.21.37
ProcVersionSignature: Ubuntu 4.2.0-16.19-generic 4.2.3
Uname: Linux 4.2.0-16-generic x86_64
ApportVersion: 2.19.1-0ubuntu3
Architecture: amd64
CasperVersion: 1.365
Date: Sun Nov 8 21:13:39 2015
InstallCmdLine: BOOT_IMAGE=/casper/vmlinuz.efi file=/cdrom/preseed/ubuntu.seed boot=casper quiet splash --- cdrom-detect/try-usb=true noprompt persistent
LiveMediaBuild: Ubuntu 15.10 "Wily Werewolf" - Release amd64 (20151021)
ProcEnviron:
 PATH=(custom, no user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: grub-installer
UpgradeStatus: No upgrade log present (probably fresh install)

[Echo Nolan (echonolan)]

Relevant line from UbiquitSyslog.txt:
Nov 9 05:12:46 ubuntu ubiquity: grub-install: error: attempt to install to encrypted disk without cryptodisk enabled. Set `GRUB_ENABLE_CRYPTODISK=1' in file `/etc/default/grub'..

I had a LUKS partition opened and had set up LVM lvs inside it. After fixing GRUB manually, the system still wouldn't boot. Ubiquity didn't create an /etc/crypttab so the system wasn't bootable. After creating a crypttab, I had to rebuild the initramfses. The whole encrypted root thing is underdocumented and pretty hard to get right.

In addition, it was happy to install without a /boot partition selected, but grub-install won't work that way with an encrypted root.