Hello Miguel
The mroute command to take care of the RPF failure should be configured only on routers that terminate a GRE tunnel, and that have multicast receivers connected to them. Remember the configuration is done only to solve the RPF failure that occurs at the end of a GRE tunnel.
In your scenario, the most likely case is that the RPF condition is met, and so you don’t need to add any additional mroute commands. To verify this in your setup, check to see if the RPF condition is met in your routers. Remember that the RPF check ensures that a route to the source IP of a packet exists using the interface from which the packet entered the router. More about the RPF check can be found at the Multicast RPF lesson.
I hope this has been helpful!
Laz