Complex sentence: During the day, ontop of the weight being carried due to supplies and armory, temperatures reached dangerously hot and humid levels, while the dampness and bitter cold of the night gave them little opportunity for rest.
Split into simpler sentences: During the day, ontop of the weight being carried in regards to supplies and armory, temperatures reached dangerously hot and humid levels. The dampness and bitter cold of the night also played a significant role by providing little opportunity for rest.