Not sure if you meant using multisig with one of the keys inside Tails or with all the keys "outside".
I use a multisig setup with all keys external to Tails (using Sparrow Wallet). As for signing: I either use a Jade plugged-in (or any decent hardware-wallet I guess) or I could use another air-gaped method (like the SeedSigner, or even a stateless Jade using SeedQR). 1
In the previous example, you could leave one key inside Tails (for convenience), as it would be secured by the encryption of the hard-drive, so in a 2-of-3 multisig, you would only need another "device/medium" to complete the signing, leaving the third key stored in a safe place for backup.
Also, you don't even need a hardware-wallet to do it. With a spare phone lying around you could turn it into a "cold" signing device using Blue Wallet. 2
Yeah, I meant signing a TX inside of tails. I guess if the computer has a few usb ports external HWW or SD cards can be plugged in to sign. I’ll have a check when I have time
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