i have been reading threads and forums about people talking about underground shelters and the cost/time it takes to build them Has anyone considered buying 100"+ sewage trunk - i.e. concrete pipe that is 100" inches or more in diameter? This kind of piping is usually buried underground, so can endure the weight of the earth on top of it...you would need to fabricate some end pieces and an entrance but that should not be too difficult. has anyone looked into this? I have tried googling for this material but cannot find it.