[libvirt-users] creating a lxc image to be used with libvirt-lxc

Dear all, I'm moving my first baby steps with libvirt-lxc trying to convert over from an LXD installation and one of the hurdles is putting together an image. All the examples I found about libvirt-lxc refer to running /bin/sh in a container, almost as if it was docker, as opposed to run a "full system" like I've been doing with lxd. Also virt-install, often referred in libvirt docs, seems to be specific/only for kvm. Can anybody point me to any documentation to achieve the same as you'd do with lxd? would it even just work to use those images ( https://cloud-images.ubuntu.com/) with libvirt? Last but not least, is there any way to "publish" a modified image so that I could make changes to any of the above and then reuse the modified one as a base for other containers? thank you, spike