When dealing with electrical appliances, safety is the most important aspect to consider.
Exposing the contact points of the e-ballast to evaporation (seawater) is very unprofessional. It will give a nasty shock! Worst, if it takes away ones life.
No matter how high you place your e-ballast in the canopy (hood), evaporation still takes place and it'll collect at the exposed contacts after sometime.
So for safety, no contact points should be exposed to evaporation.
Check out the pics of the covered e-ballast