Having recently gone through the process the details provided to me are still fresh in my mind. Disclaimer - this is not legal advice only my recollection of how the process was explained to me.
A trust has to be tied to some event in which the trust will dissolve. In my case, while myself and my wife are co-trustees the trust is tied to my lifespan. IF my wife passes before I do, nothing happens and I can continue to own the items held in trust. If I pass before she does then she will need to establish another trust to move the guns into. My understanding it at my passing the guns would need to be turned over to a licensed dealer to be held until her trust is established and the proper forms filed to transfer the guns from my (now dissolved) trust to hers. There would of course be a legal fee to setup the trust and the dealer would most likely charge a transfer fee to assist with paperwork but it is my understanding that the tax stamps would not have to be repaid for each item.
Along those same lines if she passes before me at the time of my passing the items would go to the next person specified in my trust. In my case, I have it written so that my eldest child (currently childless) would be next in line and that if no children are present items would go to a specified friend. The sames steps above would apply.
To sum it up the largest benefits of a trust are (in SC - can vary by state)
1) ability to bypass CLEO signoff
2) ability to share ownership with spouse / other parties
3) ability to pass NFA items to designated recipients at time of death without needing to re-pay the tax.
Lastly, with all of this consult your local and state laws. For example I was able to pick up a rather good deal on a SMG recently in NC because the dealer told me the sheriff in that area was not signing off on Form 4's and that NC law does not allow the use of a trust for SMG ownership making it hard to sell. Other states have no issue with trust ownership of smg's.