Usually need a lockable and moveable storeage container with a non sparking liner and a specified burst pressure strength. Most municipalities restrict one to 50LBS or less stored on the property or in residence.
Dixie Gun Works used to sell a powder magazine that would meet most,if not all, requirements around the country. I think they still stock them. I have one and also an altered refridgerater that meets local requirements in my area. Just took the cord off, installed pad locks, and viola...a moveable powder magazine with a non sparking liner and required burst pressure strength!