You need to transfer Tails to a thumb drive to enable the persistent volume, to save your key. You can't do that on a CD. LE won't find anything on your hard drive. They could find the thumb drive but they would only see an encrypted volume, not its contents. Of course, an thumb drive is relatively easy to get rid of, flush it down the toilet, throw it out the window. You could have time to get rid of it even in a raid. It's much better than having data stored on your hard drive, which takes hours to overwrite.