@staypath Yes, this is possible. I just added this recently with package v1.8.0 (so a month or so ago). There is a file called /app/data/dnsmasq.conf where you can add custom dnsmasq configuration. After adding config there simply restart the app. See https://docs.cloudron.io/apps/openvpn/#dns-server
@mehdi I agree with this. However, it would also be important to have the ability to give the container a static internal IP and allow the configuration of the VPN app to set that container as the default DNS server.