I did probe through the paper, there is not a lot of moisture loss, of course, I am using a metal skewer and once you get through the paper, it is just like probing a brisket for doneness.
There is some build up of liquid in the paper, and some steam, or at least hot air. And unless you are like me and love scalding burns and sore fingers, I suggest you handle the paper with some diligence and do not open it and reach right in.
I'm feeling bearish, and I'm packing a Wusthof Grand Brisket slicer from MABA
"perhaps...but then again...maybe not..."