I actually saw a video on mango grafting on youtube and the guy recommended wrapping all scions before grafting, this eliminates the unnecessary pressure you put on scion when trying to wrap after the graft and it also ensures tighter wrap thereby may eliminate moisture issues. May be most already do it this way, I was wrapping the scion after grafting. hereon, I will wrap the scion before proceeding with the graft, after graft, I will simply wrap the union and seal