Lxc container on nfs share

I am running lxc containers on an nfs2 share, this works very well. Now I would like to upgrade to nfs3 or nfs4 (because of the 2GB limit and better performance). But I am not able to get it running: the userid mapping hurts my brain. I do not know, which container uses which userids. And I need root with userid 0. I must admit I do not have any experience with nfs 3 and 4. Can anyone point me to some documentation on this topic?