Forming a Revocable Living Trust for your NFA items is a very good idea.
A local dealer used Quicken Willmaker to create mine for free & then I got it notorized. State laws vary, so be sure of what's allowed in your state. Find a dealer that has it in stock so you don't end up waiting even longer for approval.
I went with an AAC M4-2000. It's FA rated and attaches via the Blackout flashhider/mount, which is ususally attached with Rocksett so it won't go any where. It uses a ratchet type mounting system so it's easy to get it on/off quickly & you don't have to worry about it loosening up during mag dumps. You can put additional mounts on different 5.56 hosts, so it's not dedicated to one weapon.