A trust is the same as a person. You transfer NFA items to a trust the same as an individual. Anything a person can do a trust can do.

You fill out the ATF Form with the trust's name as the person aquiring the item. Instead of a person's name you put the name of the trust. A trustee of the trust will sign the paperwork for the trust. The trustee doesn't have to do the CLEO signoff stuff that goes with a Form.

You will have to pay a transfer tax to move something into a trust if you already own the NFA item. Same thing if you're moving something out of a trust to you as an individual.