"...If a massive natural disaster (flood, fire, earthquake) was to occur, or a man-made disaster (dirty bomb, accidental chemical release) it would be nice to have specific locations picked out ahead of time..."

Biggest problem, as I see it, is predicting where this disaster is going to occur, which way the wind will be blowing at the time, which part of the earthquake fault did what, what Mother Nature will be doing during each season, etc. Not knowing that, one would have to have several (or a lot) locations pre-picked. Pretty soon it could become a deal of telling all the family to head to spot 13Q or something. Hard to remember and keep track of. And on top of that are those pot farmers...