larryd:
Water will get in.The moment you drill a hole in a case, the case is no longer water proof, guaranteed.
It does not need to be submersible. Its going to be is a semi sheltered area. But regarding water getting in where you drill for a connector, I've done it many times with no water getting in. All you have to do is put some flexible waterproofing compound under your washer, make sure the hole isn't badly over sized, tighten the nut until the compound squeezes out, and clean it up with a paper towel.
But more important for my project, where contacts meet in a connector is the place where various kinds of corrosion occur, hastened by a humid outdoor environment. Thats why I need a waterproof connector this time.