Mwan3 and GRE tunnels

I am looking at leveraging the work in mwan3 to work with GRE tunnels. The documentation mentions that it can work with OpenVPN client tunnels, but only talks about aspects of the configuration. Looking at the example mwan3 config file, with GRE I should not have to split the IPv4/IPv6 into separate interfaces. Is there someone who could provide configuration advice on mwan3 with GRE?