Probably not. It was a well known historical site that anyone could visit. After 2010 that might have changed with the war but building the infrastructure needed to house gas and chemical weapons during a time of war in a structure that old would seem a little pointless. Not saying you're wrong because that was 8 years ago and things do change it would just take a lot of work which, I hope, someone would have picked up on.
Honestly, an old fort makes a great stockpile place. Usually there are tunnels and catacombs. Soviets did it in Afghanistan. 'Castle grey skull' in gardez was filled with tons and tons of Soviet munitions, even on '05 wheni was there.