@Gui , please make sure you has "--external-ip=18.104.22.168" as part of the command when running p2pool. This ip will be send out to other p2pool node and advertised as public p2pool node for others to use, then p2poolnodes will list your ip on the page automatically.
I guess you already checkout https://github.com/dashpay/p2pool-dash , let me know if you have any questions.
BTW, you could join Dash-Nation Slack ( https://dash-nation-invite.herokuapp.com/ ) for more helps on #mining :)
Dears, as posted by @chaeplin on Dash-Nation Slack:
Information about transaction malleability https://en.bitcoin.it/wiki/Transaction_Malleability
Our related changes for BIP66 https://github.com/dashpay/dash/pull/178