Think of your objective for storage.
Is it to keep them safe from theft?
Is it to keep them from children/guests?
Is it to protect them from damage?
Any storage is usually better than none.
Getting better storage than your last method of storage is better.
Temperature Change and Humidity is your enemy.
Large weasels can be dangerous.
I have used cases for extended temporary storage. Clean 'em, Lube and Protect them (CLP?), keep them in a stable environment. (Closet, etc)
As Axxe says, they don't make good long term storage as far as the gun sees it. A locked case when kids are around is great storage.
My first storage was a plywood box (locker) I made. It's primary purpose was to ensure that my new step-children were separated from them until we had some education and respect of firearms. It worked well for it's intended purpose. I did not use the box as primary theft protection.
A good safe can be purchased for the price of a quality firearm.
Mine is securely bolted into concrete. I just bought a heater strip for it. My guns are happier now, I am happier now. My wife, grown children are happier now.
We have 9 grandchildren that visit regularly. I am teaching them to shoot, but we all rest better knowing the guns are happy.