So you want to run Whonix inside Tails? I swear if you hang out on this forum long enough, you'll hear everything. Why do you want to do this? What benefit do you think it will give you, that for example, running Whonix on your main OS, where the virtual hard disks are already stored, won't give you? It *may* be possible. If you log in through the admin option, you may be able to install VirtualBox from the Debian repos. I honestly don't know, because I've never heard of anyone doing this, and Tails does some nonstandard things, like with networking and filesystem mounting, and possibly kernel modules, so I don't know if VirtualBox will work. I don't know if it will require special configuration, and what that would be. In order to use VirtualBox, you'll have to instal the kernel modules, and I don't know if that's possible.