Depends on the time of the year. In the winter when its dry I definitely give them a mist. In the humid summer a little wipe of a damp cloth on the cores is good. Never had any problem with warping if you leave them cure long enough under weight 15-24hrs. I think a mist makes the glue foam a little more and penetrate better.
I would think that bagging and vacuming them should draw just about all the moisture out. Thats how we get moisture out of a/c systems is by drawing a vacum.

Either way the urethane glue is some good stuff and so much easier to work with then epoxy.

It works for me.

Wayne