on the topic of fumes, ive read and i believe its mentioned here as well, that its best to wash them off and let them air out for about a week or so allowing them to release most of the toxic stuff, i assume that the heat wont be problematic once its been cooled off and aired out the first time.
Yes, I would recommend washing and letting dry out for 3 days or so. I have been successfully using these and they have been standing up quite well.

As for heat? I have not heated them up. My cresteds temp are always under 85 so heat has never been a problem. However, when cleaning with very hot water they can tear much easier, just a side note.