I have a page in my trust that specifically names my wife as co-trustee. This page must be notarized with the settler's signature. Then there is yet another page for the co-trustee to sign with witnesses, but that page does not have to be notarized and is not required for the trust to be legally binding.
I went this route to avoid problems with the suppressor being in my wife's possession when I'm not around or in case she wants to use it at some point.