I've thought about this a lot. I thank you for braving the flames to discuss it.
A basement is a natural choice to me, especially since we have one, but don't have any property out in the country, or the money to construct a
purpose-built structure.
I like the idea of making the home less attractive and more run down, but that's only one important aspect of it for me. Camouflage is natural, bugs
do it, we should do it too. Psychological most often, it would seem.
A fake wall seems like a good idea...of course, a way in, that is able to be secured and a way out in case you need to run.
Here's a site for hidden doors. I'm taking a different route, which I would share if I wanted to, but I don't.
www.woodworkingcorner.com...
I think the most important thing is to make it seem like there is nothing there...a lot of homes have basements in this area, so I have to think a
little differently about it, because a basement would be EXPECTED in my home. I think in a case like this, it becomes a question of sectioning off an
area and concealing it.
What stinks, is that this is not going to help you in every case. You would need a purpose built shelter for some of the more hardcore sit-x
occurrences. I think if you can get a good seal, a source of freah, hopefully filtered air, fresh water, warmth, food, medicine and a way to see what
was going on outside, you'll be good for most anything short of nuclear or particularly nasty biological incidents.
I hope you get some good plans and share them with us.

Good luck!