Advice please: SE Asia trekking as a beginner
In late June/early August, I'm going on an 18-day school trip to Cambodia and Vietnam. Some of it will be city tourism & hotels, but there will also be trekking & camping. My school is collaborating with a company that specialises in school expeditions, so we'll have an experienced trip leader, but I'm still nervous about the trekking, as I'm inexperienced.
How do I combat the heat without adding too much weight or taking up too much space in my rucksack? What kind of clothes should I wear? I've heard cotton is good, but since it'll be a humid environment AND the rainy season, I'm having doubts. It supposedly absorbs moisture and dries very slowly, which sounds counterintuitive. Are there better options? Also, and I apologise if this sounds stupid, should I wear shorts or trousers? My intuition is to wear shorts, but I ask because I often see more experienced hikers wearing trousers, even in the heat. Anything else I should know?
Please go easy on me if I said something silly! I'm a beginner and a teenager, so I really don't know what to expect. Below is some potentially relevant/helpful info:
The main bulk of trekking will be over 6 days/5 nights, roughly 20km each day. It's in a rainforest/mountainous environment. Backpack is 65L (we have additional 35L backpacks, but I'm not sure if we'll bring them on the trek).