Until bind-directory functionality is completed upstream and implemented as /usr/lib/qubes/bind-dirs.sh, files & directories can be added to the BINDS array in /usr/lib/qubes-whonix/bind-directories to have them persist across reboots.
Example: Persistent OpenVPN Configuration
Open File as root: /usr/lib/qubes-whonix/bind-directories
Add entries to BINDS array:
need to exist in the templateVM and the way to create them is to sudo systemctl enable openvpn... So no point in binding what is already in the Template. There could be a point in binding these files if they could then be deleted in proxyVMs that didn’t need openvpn but that’s not possible either:
 Files that exist in the TempalteVM root image cannot be made deleted in the TemlateBasedVMs root image using bind-dirs.sh.
So: use dedicated openvpn TemplateVM or standalone VM. Template still has advantages: 1. non-persistent root fs, 2. per-proxyVM openvpn .conf
Actually, it is possible to enable openvpn per-proxyVM if you bind the directories instead of the files: