One of the great things about a well written gun trust is that it can be created to deal with multi state issues. Many people move and even include co-trustees or authorized users who move or are in other states. If your gun trust is only written to deal with your state laws, the chance that it will provide incorrect or misleading advice to others involved with your trust is increasing. We see these issues with many online trusts.
An ATF Form 20 is not required when you move states. A Form 20 is only required for Title II firearms other than suppressors. That being said, I recommend completing a Form 20 even for suppressors. For those of you who have our gun trusts, we include a section in our instructions that goes into detail on this topic. Most police officers do not know that suppressors are legal (yes, I know this is hard to believe). Given that, I would much rather have a document from the federal government (the form 20) stating that I or other members of my trust are permitted to be in a state. It is much easier and less expensive to have these issues resolved before you are detained than after your items are taken or you are detained.
With this in mind, you may also want to get a Form 20 approval for traveling to states and not just for a change of address to another state. A Form 20 is not required if you are staying within the same state, even if you move within the state. A well written gun trust will include information like this and on other common topics that come up over time.