Locust??? They grow like weeds around here. I use them all the time a fence posts and for other "things". To bad we aren't closer I could send ya a few for your roof...
We might look into the bag construction for a root/storm shelter. I really need one and it sounds cheap enough. The idea of the "stucco" for the covering would work great for the inside also.
"Yea, though I walk through the valley of the shadow of death, I will fear no evil: for thou [art] with me; thy rod and thy staff they comfort me." Psalm 23:4