I have just typed a letter listing all my registered SBS, SBR and cans (individual and trust) and mailed it in when I have moved in state. I recently sold my house and we are in a tiny rental while we finalize build plans. I kept all my NFA items with me and had to store everything else at a relatives house due to no room. The letter I sent just said everything would now be located at my current address. A few weeks later I get a letter back saying basically thanks for letting us know.