One more thing - make sure you have at least one key type padlock on the door and not just a combination lock. I recomend two locks. This way when someone says "Oh really, guns huh? can I see your gun collection" you can reply:
"Oh sorry but that key is on my other key chain that I left at work, or left at grandma's house, or left at the gym, or up my ass, or anything other than it's handy and available here and now at the moment if you catch my drift. I once had a similar locked closet in my garage where I kept my "firearms and amo" and it stayed locked up safely for over five years. Nobody ever really asked questions and I had lots and lots of visitors. Also, being a christian I do not ever lie about anything. My guns and amo where in fact in that same closet.

bob