He was around 50 years old when he surrendered, I've read somewhere else that medics who examined afterward said he had the physiology of a 20/30 years old man He mostly ate raw, in order to avoid making fires, to not get spotted What the vietcongs did against the US army in vietnam is also rich in terms of "know how", how things should be thought/conceptualized in general when it comes to long term survival against all odds, for cheap You have to have the environment going for you, preferably, phillipines or vietam's jungle aren't siberia, to begin with, it's not a desert in terms of local resources Now for the bunker part, there are cheaper ways than all concrete or metal things. Earth bags/sand bags for instance, pretty reliable, battle tested https://www.youtube.com/watch?v=kAoBVPyvhC4