Tennessee law is modeled after other states laws in regards to NFA items. Tennessee law allows a defense to the crime of possession of an NFA item (not made in Tennessee) if the NFA item is registered to the "PERSON".
TCA 39-17-1302 (b)(7) Involved acquisition or possession of a sawed-off shotgun, sawed-off rifle, machine gun or firearm silencer that is validly registered to the PERSON under federal law in the National Firearms Registration and Transfer Records. A person who acquires or possesses a firearm registered as required by this subdivision (b)(7) shall retain proof of registration.
The unincorporated trust is not a person according to the BATFE and the GCA. So it would seem that being authorized by a trust to possess a NFA item is not a defense to the felony of possession.
This is just a thought and could possibly be a problem for a trustee in possession.
This is not related to my arrest last year for illegal possession of a silencer that was registered to my person for which I possessed a form 3. In that case I was indicted this May and the state of Tennessee is proceeding with it's prosecution despite the fact that they have a copy of the approved form 3 which transferred the NFA item to my person.