As I already talked in previous post about creating and maintaining a Gentoo Backup, now I've created a script to make it really easy to unpack, mount, umount, chroot and compress any gentoo stage3 for backup purposes (specially useful to test packages when you don't want to make a live system dirty if something fails)
It is available on GitHub with even an ebuild to be put on an overlay to install it.
It works in command line interface with interactive menus to be easy to use with no parameters added to it as them are usually forgotten by users.
Also, it will be configured to use a folder you specify, so if you don't try a vital folder, it is 100% safe to use it, as it will not write to anything outside specified folder.
Currently, it is beta, so it could have some bugs, depite I've tested it and seem to work, for feedback, write to stormbyte at gmail dot com email address and I wil try to help.
Hope this is useful for gentoo advanced users.