I use an Ikelite rig, my concerns re salt crystals are solely in the push buttons. Salt water gets trapped in these and only dries slowly and may take a week out of water to become supersaturated and start to crystalize, I believe it is vital to remove all salt from within button holes before prolonged storage (more than a couple of days). Therefore:-
I may dunk after a dive but don't obsess about it, at the end of a trip before flying home I will get a tank of fresh clean water and reassemble housing without camera and repeatedly press buttons and use an air nozzle from my reg to dry out water before dunk and button press again. Repeat thrice.