When you have a tax stamp in your possession, is there some sort of storage requirement for keeping those items at your house?

For example, if I turn a shotgun into an SBS, am I required to keep it inside a safe when I'm not using it? I realize that ownership of an NFA item requires great responsibility, and a safe would be a great idea. I'm just wondering if I am required to buy a $1,000 safe to put a $400 gun into.