Best way to waterproof self righting floor chamber? boat in PETG in 2 parts

[Christophe]

Hi, I have printed in PETG a boat with a self righting flood chamber. This boat is 40cm long in total and printed in 2 parts of 20cm, so the flood chamber can currently be accessed thanks to this cutting, until I glue both part together.
What is the best way to treat this flood chamber to prevent any water from leaking inside the boat?
I am not just talking about the fact that I need to glue both part together, I am also worried some water can enter through the PETG wall of the floor chamber inside the boat. The external hull will be post-processed helping to ensure it is waterproof, the flood chamber is not concerned thus my question.