I am an attorney for a court and I work with guardianships. Our state laws give us the authority to set up trusts for those under guardianship (or as an alternative to guardianship) and we routinely create trusts which are special needs trusts with assets that belong to the person under guardianship.
I assume that you are creating a special needs trust with your own assets or assets that will be in your estate when you pass.
I don't know that I can answer a lot of specific questions for you, but having an attorney do this is the right way to go.