Things have changed so much since I did U/W photography.
10 years ago digital was quite basic and limited - and no TTL available. But then again - anyone shooting film underwater knows what he is doing
Perhaps you know of this -
There is a company in Italy (if memory serves) that makes a universal housing - different houses - and each fits a range of cameras of similar size - (eg D800, D810 etc) and you have them "chip" the body for the particular camera. It connects the camera controls to the housing controls. If you upgrade - you just get them to chip the housing for your next camera. Saves a helluva lot if you don't have to keep buying houses every time you upgrade a body.