Todays gas is so poor that it does not  vaporize like 30 years ago,,,, BUT IF you get a leak inside a enclosed area & get the right mix, it still can go BOOM EASY... I'd check with your insurance 1st . Insurance may not like it. I think the Fire marshal will blow up if he saw a bulk tank in a enclosed building.  I was told that when I was doing my containment  NO WALLS, & they did not want a roof either. But I wanted to keep the moisture out as well as I could.  Roof is 18' or so with rain gutters. Going to be hard to keep any vapor in.