In a recent, impromptu test, the Canon C300 is not suitable for use while submerged or enveloped in Pacific Ocean water. Due in large part to electrical devices not being compatible with a mixture of hydrogen and oxygen, it is highly recommended that one keep these items separate. We here at F11 Rentals rarely find ourselves working under the sea, and thus, do not have use for an underwater housing for the C300- it would have been helpful in this situation.
In conclusion, C300 Mark i + salty, ocean water= bad news bears (shout out to Walter Matthau).