I did it from a terminal just before starting the installer, because i wanted my personal setup with the labels i choose.
I did shrink my Windows system partition, purge the two partitions they used for recovering and resetting this Windows with gparted and created a new primary partition for /boot and a logical partition without any filesystem.
Then i went to the terminal and created the encrypted container for the LVM.
cryptsetup luksFormat -y --cipher aes-xts-plain --key-size 512 /dev/sda5
cryptsetup luksOpen /dev/sda5 crypt
vgcreate cryptVG /dev/mapper/crypt
lvcreate -n root -L 15.5G cryptVG
lvcreate -n swap -L 4.5G cryptVG
lvcreate -n data -l 100%FREE cryptVG
That created 15.5 GB space for root, a 4.5 GB swap and all the free space for data. If you want you could apply the file-systems now, but the Installer also might take care of it. Now close the crypto- container.
cryptsetup luksClose crypt
With these steps the preparations are over and the installer will pick everything up, ask for the passphrase of the encrypted partition, show you all the logical volumes and let you also choose a custom mount point for the data, like /home/$USER/data or /media/data. All the logical volumes do need no encryption, because the containing partition is encrypted.