i don’t know anything about raid, but judging by your manual command to unlock and mount it shouldn’t be any different than my non-raid extra encrypted disks setup.

it should be just adding it to crypttab and fstab and a keyfile and grub config edit maybe, and if you mess up you can still get in to edit these to try again with a liveusb (easiest way to go back to previous setup is just comment out the lines you add) and manually unlocking and mounting like you are now anyway, so don’t be scared.

https://wiki.archlinux.org/title/Dm-crypt/Encrypting_an_entire_system

is a lot but the specific info you need for your setup should be various places there and linked there. good luck!