Currently adding extra configuration in PV_LXC_EXTRA_CONF result in sourcing the value content directly without any option to define multiple lines in the configuration file.
For example an array of strings like:

"PV_LXC_EXTRA_CONF" : [ "lxc.mount.entry = <mount1>\n", "lxc.mount.entry = <mount2>\n" ],
will generate the invalid lxc.container.conf output:

[ lxc.mount.entry = <mount1> lxc.mount.entry = <mount1> ]
The issue is how the value is sourced in the template file: https://github.com/pantacor/pvr/blob/master/templates/builtin-lxc-docker.go#L156
Is very hard to work with a very long line in configuration files. Is better to split the extra conf with an array of strings. Other options like PV_LXC_CAP_KEEP are actually handling the elements as key:value which makes the split possible.