The Moulthrops soaked their bowls in polyethylene glycol to avoid cracking. They (or at least the elder Moulthrop) would take a section of a trunk and turn a bowl out of it. Some of them were several feet in diameter. I have also read of people soaking bowl blanks in alcohol. Since you have a bunch, you could experiment with different methods. If you check with AAW, they may have a plethora of ways to avoid cracking of blanks.
Roy G