After many days of banging my head against how to get 18.04 installed with raid1, crypt, and lvm on new disks from alternative server iso, the crux was the 1mb bios boot partition at the beginning of both disks.
Without that I’d get all the way through the install and – can’t install grub “you’re f’d”
What I did:
partition 1mb bios boot partition 1mb into the disk – offset by 2048 bytes from beginning of disk for size of 2048 bytes. type is bios boot.
then I did a generous boot partition of 732MB as raid, then the rest of the disk as a raid partition.
setup raid on sd[a,b]2 as md0, sd[a,b]3 as md1
setup ext4 on md0 mount as /boot
setup crypt on md1
setup lvm on crypt
setup swap on lvm, setup root on lvm
assign swap as swap
setup ext4 on lvm-root mount on /