I got a lock-box in the sporting goods section of Walmart for $30. It has a cable hasp in it. I cable-locked it to a stud in my bathroom linen closet. Under about 10 sets of sheets. (Just gave out my secret to thousands...) Oh yeah, my pet cobra sleeps in the sheets. THERE!
It's not burgler proof, but it would take one hell of a bolt-cutter, and a pure luck to find it.
It's about 6" tall, and 14" deep, and 7-8" wide. It hold 4 handguns comfortably.