Well, it worked
I put the pocket back on him this morning as he hadn't even peed in it when I took it off him last night.
No red skin or any sign of soreness and, despite drinking loads whilst we were shopping, no leaks!! So, now he's in the other one lent to us. If that also comes off and leaves no red marks, I will buy 5 or 6 preloved ones.
The WNNN also worked. It was wet, but not soaking and no leaks through his woolies