Isn't Tails' main feature that it is amnesic and doesn't leave any data between sessions (aside from opt-in persistent storage)? Or any other live OS would act in the same way?
If it's not explicitly designed to do so, another LiveOS might allow some session data to survive, but this is only possible if using a writable medium like USB flash (and hence why I mentioned using CDs as a failsafe; you don't even have to worry about Tails having a data persistence bug if you run it from a CD, it's not possible for any data to be written to the CD accidentally or by design)
1. Download Tails, and make a bootable USB with it.
2. Boot Tails on an offline computer.
That works, of course. But there's no particular reason to use Tails, since you're staying offline. Tails is only different from other live os'es when using it online, any live os would work for this purpose.
But Tails Linux already has Electrum as part of its set of tools that is already pre-installed.
Ah, I didn't know that.