I have not had much luck with bark of any kind. If you stop and think about it, the primary purpose of bark on a tree is to protect the wood inside for exterior elements. As a result, I believe it has properties that prevent it from being able to be stabilized well. Think of bark as the tree's rain coat! I myself have not had much luck stabilizing pecan bark as well as a few other local species. I also tried some cottonwood bark from your neck of the woods that we got on an Alaska trip a number of years ago. It was before I was really involved with stabilizing and before I knew what I know now but I did not have very good results. Maybe someone else will pop in with a different view that has actually done it recently.
I am not sure about the cottonwood bark, but I have used Cactus Juice to stabilize some porous material like 'bear jaws' and other critter parts successfully. I have seen corn cobs stabilized for knife handles. There is also a process called 'resin casting' that may work for your wood.