Well, I'm glad you guys have been able to teach the Nissan engineers how to vent a differential properly.
I don't off road so won't even say anything about it. But, I do a lot of fishing and boat launching.
If it's necessay for you to back into the water so far when at the ramp as to submerge the differential you have a problem. As I'm certain you know how best to deal with a launch ramp it's clear that the ramp design is bad and there is nothing wrong with your technique. I'd look for another ramp.