Most of our lights over here are of the submersible type.
They started of with the "bell jar " type which never seemed to work as promised and corroded easily.
However now ,with the sealed units and even LED submersible types, it seems to have solved the isssue.
The still recommend disconnecting your plug from the tow vehicle though when launching so the cold water on contact with a lit unit does not damage.
Do have running lights on trailer frame but never get submerged , so cheapie bulb fixtures work equally well.
Would hate all that routine of putting a light board on