The hull has been filled with a closed-cell PUR foam that will stay afloat forever.
As the foam is a good thermal insulator and the batteries generate heat when charging, there are several vents leading to the battery tubes to prevent overheating.
The two compartments that are not filled with foam will be completely separated from each other. Each compartment is equipped with a flood sensor that will transmit alert message in case some water gets inside.
The servo is wrapped with a rubber glove filled with a silicone grease as an extra layer of protection.