Please don't ever use a QC4. There is no justifiable reason. QC6 on the other hand, all about.Because it is a QD rather than a QC4, I connect before getting in the water. I don't think it would be the end of the world to plug in inwater since it is just going to an OC 2nd stage, but still, the less salt in there the better! If I were in a situation where donning in water was the norm, I would swap to a QC4 and have the split hose system others are recommending to get the connector mass off the BOV.