WARNING: Do not upen your underwater camera case outside.
REASON: The warm moist air will get inside and then when you put the camera into the cooler water, the moisture will condense out and cover the inside of the case with tiny droplets. This will effectively cover the lense of the camera and you will end up with no usable pictures. Luckily I found this out after our snorkeling trip when we were playing around with the camera in the swimming area, so my snorkel pictures are fine.
RECOMMENDATION: Only open the camera case inside where the air conditioned air is cool and dry.
Next time you buy a new pair of shoes, keep the little silica gel packets that are in the box. Those little things are there to capture moisture. Place one or two of them in your regular camera case and/or underwater camera case. They will keep the condensation from clouding your lens when you go from the air conditioning to the humid, outside air.