Thanks for all the advice, I'll what else I can come up with. I thought also about putting the warmers in the lining of my bag. My bag has in insert that all the gear goes into and can be removed from the entire bag, that way if I put a few warmers between that insider and side of the bag it might keep the overall bag heat up but wouldn't be directly on the camera itself. I mainly want to keep the bag temperature up so the camera temperature doesn't drop to much going from the parking lot to the greenhouse on very cold days. Then if I go to the temperate house first and get used to the humidity and then on to the tropical area, I was hoping it would lower the potential for fog or condensation. I just didn't want the shock of going from 15-20 degrees at low humidity directly into 80 degrees at high humidity.