I’d say the in this thread referenced sources are the howto for now. Purism writes about the integration:
we are working on adding a script upstream to automate the process of configuring your root LUKS partition to use a Librem Key
Any howto written now, would be obsolete when the script is upstreamed.
Anyhow, consider this:
Why do you want to use your LibremKey on your encrypted drive? If it is to gain some security I’d advice you that you should first understand what you have now.
There are threads about the setup you probably use that discusses possible security problems.
If you want to increase security by enhancing your setup you need to take the time to understand what you’re doing. You have all tools at hand, but you need to learn to use them, you need to take responsibility over your data and data security.
Just think about the possibility that you’ll break your setup (while changing it or at some point in the future) and you’ll not have the understanding to get back your data and the access to your workspace.
If you’re willing to walk that path I can assure you that you’ll get help and information here - at least that is my experience here.