I'm planning on buying a short-barrel upper for my 9mm CMMG guard. At some point I'll do an NFA trust, but short term I'll probably SBR my lower as an individual. I understand that my wife can't use the SBR (she has no interest). I'd guess that she cannot have access as well. For example, she no longer can have access to the safe, but to what extent would this extend? Does the SBR have to be in "my possession" at all times (or secured by a means to which only I have access)?