"oceanographic connectors" etc. There are many different types of waterproof electrical
connectors used in the research
business. Businesses that sell oceanographic instruments also sell these connectors. I saw one today that costs $5000 for an acoustic array being tested. Don't let that freak you out though.
There are much cheaper ones.
I have also taken some male-female insulated crimp on spade connectors, packed them with silicon grease and then wrapped them with self-annealing tape...it works. The grease displaces any water
that might get past the tape. Tef-Gel works as a substitute for the grease and Densyl tape can work as a substitute for the self-anealing tape.
A third alternative is this: DRYSEAL CONNECTORS
These I would pack with silicon grease.