[dredmorbius]

With a sufficiently low-power system, purely conductive/convective cooling should be sufficient. You'd be looking at a finned enclosure, possibly with a directed airflow over that.

The real problem is providing for ports (power, networking, comms) without penetrating the enclosure. The recent Marianas Trench submersible showed a number of connectors designed for very high pressure environments, something along those lines should be sufficient.

Grounding would deal with static.