We use some padded ESD bags that fold around the board and close with velcro.  We call them ESD diaper bags.  The advantage with these is that the padding prevents damage from handling or stacking.  They are likely more expensive, but we have a service to sort and re-use them (or at least used to).  They'd also allow gasses to escape.  I don't know where we get them from, but can look it up if you're interested.