Anouther example of why a fixed position dosn't work, look at the Sigfreed line as an example. Just about the strongest possible fortifications you could imagine, but it still didn't work. Fixed cache is fine but don't depend on a bunker for a defensive position, it won't work for long. Fix position is fine for survival porpouses if you have no out side detectible source of smoke or have a really well hidden entrance and exaust/intake outlets, and don't allow any confrontations in that area prompting an area search.
Always fight from a moveible position far from any cache or home bunker as possible, good old gorrilla tactics. If ya really feel the need for a bunker, go for it, but don't draw any attition to it or you'll loose it. That's where the NVA always screwed up, they'd fight back to these positions making it easyer to locate them. Evaide and escape is the way to go, and only go back for resupply or to vanish, never fight from there or otherwise draw attition to the area.