be careful with plastic covers. while there isn't a danger of fire to the paper at that temperature, the plastic could become warped.

i would test with one book that you were going to throw out anyway before stacking a bunch of them. you can choose to go with even lower temperature, but you have to increase the time considerably (~double the time for every 25-30F, but there's point where the temperature just isn't high enough to denature the proteins, I forget where, though)