I am trying to figure out how to implement this scheme:
Two persistent linux installations with full disk encryption on a USB drive.
I want this to appear to be a single encrypted volume (i.e. use a hidden volume for one of the installations) for plausible deniability.

I would probably use Tails for the OS in the non-hidden encrypted volume.  There isn’t a specific reason to encrypt Tails since it is designed to forget all sensitive data, but I want it on my USB stick an I don’t want a three OS install if two will do.

The hidden volume would be Debian or Ubuntu.

I would also leave a small FAT32 partition so that the drive could function as a standard USB drive if needed.

I can’t find any written instructions for this kind of installation, anyone have suggestions?