I've done something similar, but in a cleaner place, and for less time. My advice to you is to pack at least two outfits, one with shorts and the other involving longer pants, and to try to pick the material in a way that would benefit you here. For instance, while some types of chinos may be comfortable, even breathable, jeans would prove to be more durable in a place like S. America (goddamn--have fun, by the way).

I ended up not being able to totally decide on one or two outfits to bring, but I had the space available in my pack to take 3 skivvy-rolled looks (as a single skivvy-roll contains socks, underwear, pants, and a shirt to match) along with the one I was wearing. I brought some rolled up shorts (because I went to Greece), these thick vintage-labeled J. Crew pants (because I went to Iceland), skinnier black denim jeans (for going out in C. Europe, worn almost rarely), and some asos chinos (very comfortable for traveling, but they rip and tear easier than skin and repairs are unreliable), all paired with comfortable t-shirts to match. I also brought a dark hooded jacket that went well with everything, but I don't think you'd need one, not at least for anything but rain.

It'd also be dope if you had a nice leather belt which matched your watchband and a pair of nomadic-lookin' boots. I never tried this traveling because I'm unimaginative and could probably only make that work with really expensive boots, an Orion belt and a Timex. I stick to the frugal side of things, so (in the EU) I had a cheap belt that functioned well enough, a quartz watch that broke in Italy, and shoes that fit the description of the belt.

Just, for a word on shoes, consider putting durability before fashion, but interpret that. Picture rain, mud, small sharp rocks and walking for hours. I had canvas shoes with me when I went to Europe and leather tennis shoes with me when I went to Thailand, and while the canvas shoes became full of holes and lost their soles, they were always more comfortable than my tennis shoes. However, the tennis shoes looked better and were far more hardy, I still fuckin' wear them. So I went with those after some experience with the canvas shoes, but find out what you like.

I apologize for making this so long winded, but if you find clothes that you like wearing and can be worn every day anyway then I feel like you're already going to mind them better subconsciously, that you'll learn to move with them and stuff and not break them as easily as you would new shit that you're still breaking in.