It all depends on if you want to have the battery serviceable. In this case a simple 12S balancer plug would be enough.
In case you’re planning to build a housing for your system that is harder to service, and/or you plan to leave your battery in the housing to charge it, a simple solution would be to use a waterproof balancer port.
Use the search function and you will find many successful battery builds like this one by @Flightjunkie