I have been using Ubuntu for a few years, but aside from a little bit of playing around it's pretty much the only Linux based OS I have used. To my understanding, Xubuntu, Kubuntu, and Lubuntu are just Ubuntu with different desktop environments and default applications. The Lubuntu page on the Ubuntu wiki specifically says that, and that it shares Ubuntu's repositories.
A while ago, I started installing Gentoo on my Xubuntu box, using a chroot from Xubuntu, following these guides: https://wiki.gentoo.org/wiki/Handbook:AMD64 http://www.wikihow.com/Install-Gentoo-Linux-from-Ubuntu
I decided to bootstrap my Gentoo install following instructions outlined in the Gentoo FAQ, and after some minor difficulties, I managed to succeed.