I put a post on my blog about shipping containers but this sounds a lot better, safer, and cheaper.
If you have looked into bunkers you may have read a lot about using shipping containers to do build them out of. I need you to read this article why you shouldn’t bury shipping containers before you read about box culverts. It will make more sense if you do. Here’s my link for getting shipping containers if that is something you may want to do.
You pay out of your nose for a reinforced shipping container that you hope doesn’t get rusty and leak over time. For a typical reinforced 10ft shipping container you could probably pay about 10k. For the same sized customized concrete culverts you are looking around 6 – 8k.
This leaves you around 2 – 3k dollars to spend on better air filtration or food and water to stockpile in your shelter. Concrete will withstand blasts better than an old shipping container too. People always tend to miss that point! Check out the link about these culverts and be sure to read all the comments. A lot of great information there.
A diagram that you will find when you follow the links.