"Or just register it with the fire dept and hope the government doesn't come knocking because you have a storm shelter."

LOL.

I wouldn't worry too much about it. Most fire/rescue departments are holding bake sales to keep the rescue equipment in tires.

They don't have a lot of spare time or energy left to run a 'shelter detection, reporting and exploitation division' to take full operational and strategic advantage of your converted closet or shed. Making it into a regional command and interrogation center where the war against the noble patriots and rebels is run from and innocent victims are are water-boarded for fun and profit.