Setting up the drive

1. sudo cryptsetup luksFormat /dev/sdx1
2. sudo cryptsetup open /dev/sdx1 <name>
3. sudo mkfs.btrfs /dev/mapper/<name>
4. sudo mount /dev/mapper/<name> <mntpoint>
5. sudo umount <mntpoint>
6. sudo cryptsetup close <name>

Using the drive later

1. sudo cryptsetup open /dev/sdx1 <name>
2. sudo mount /dev/mapper/<name> /mnt
3. sudo cryptsetup close <name>

Just be sure to sudo cryptsetup close <name> when you're done