I can’t speak to the SOT, but upon your passing your estate can transfer any NFA items to your beneficiaries and I’m pretty sure that they pay no tax for that transfer.
Trusts used to be very beneficial, but now they serve only two purposes that I’m aware of. Most importantly, they allow several folks, each listed as a co-trustee or such, to have possession of an NFA item, so for example your wife could go shooting with a suppressor and without you. These folks are all Responsible Parties in ATF language, so you’d submit fingerprints and pics of each if they are in the trust when you add an NFA item.