The current "press Space to enter Port Battle" mechanic is a quite "raw".
My idea: 10 minutes before a Port Battle begins, a group selection window should appear, accessible to trusted guilds. Members can mark themselves as "available", while the attacking and defending admirals can then select which members to bring into the Port Battle.
Once the preparation time ends, the selected members of both the attacking and defending guilds will spawn at their respective spawn points.
Image is an laughable example made by AI