Talk to a lawyer about doing a Revocable Living Trust. Then ask them if they know anything about the NFA. If they do then give them a quick quiz as to transferring, setting up checking accounts for the trust, and get a thorough run down on what the trust will actually do.
The main thing the ATF wants is for your Trust to be a legitimate Trust, not just some document you got to get around the CLEO signature. The next part is they want to see you have legitimate and reasonable methods and terms for the storage, transfer, future transfer, and outlining of Trustee responsibilities. You have to send in a copy of your actual Trust now. A memorandum of your Trust will not suffice. Again get a competent Attorney to do it and be safe.
Do you have to have all those NFA friendly terms and conditions. There is no certain answer from the ATF unfortunately. They only really say in their handbook that they will allow the use of a Trust. I like all the terms and conditions in their to protect the validity of the Trust, the Grantor, the Trustees, and the beneficiaries.
Some lawyers will tell you, you can do "A" and some will tell you, you don't have to do "A." Remember, get an Attorney to do it. Why? If something goes wrong you want someone you can sue, and while the ATF may not be sympathetic to your honest undertaking, a judge might. If you do it yourself and you do it wrong, you are out of luck.
When it comes to the ATF you can't be too careful. If you ask the same question five times, and get two different answers. You go with the answer that is least likely going to get you in trouble.
I do Personal Injury in Florida mainly, I got into Estate Planning because one of my old professors liked my ability to talk to people. So on the side I did Trusts and Wills(plus Power of Attorney, Healthcare Surrogate, etc..) till a buddy asked me to do an NFA Trust for him. After three months of research, and calls to the ATF(plus letters), and a whole host of other annoying things I came up with a twenty-five page monstrosity for him. Then a buddy of his wanted one, then his father's friend wanted one, then his second cousin removed wanted one, etc. etc. etc..
They all complain that the Trusts are too burdensome and that other lawyers have told them they can get a Trust without all the headaches. To that I would say "then get it from them." So if you are prepared for some minor headaches a Trust is a good option.
If you want a lot of headaches then get an LLC. I've had folks with LLCs jump on Trusts once they understand them. With all that said, get a competent Attorney in your state to do it, also do your own research and read through the ATF handbook with a careful eye. If the Attorney can't answer questions you've come up from the ATF handbook then that ought to be food for thought. Again, get a competent Attorney.