Ignoring double natting is not a good idea if you ever want to do any kind of port forwarding - you'll find it won't work.
As an additional step to your guide, if it's possible, you should put your second device in the DMZ of the Vodafone router. This will pass all firewall traffic from the Vodafone router unhindered to the second device which can then do as it wishes with it.
An alternative would be to open the port from the Vodafone router to your second device and then from your second device to your target device - the end result is the same but with this option you need to open up ports on both the Vodafone router and your own router.
DO NOT do the DMZ step above if the second device is not doing Network Address Translation or you open up your internal network to the outside world!!
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