I finally came across what I think is an excellent solution and it didn't cost me an arm and a leg! I went with an upright utility cabinet from Black & Decker (SpaceAir Collection). Mine is 70 inches tall, 15 inches deep, and 27 inches wide. It's made out of sturdy plastic and most importantly it's lockable!
Read full article here:
https://www.replicaairguns.com/2011/2/14/safe-air-and-blank-gun-storage-unit-on-a-budget.html