We have our deeds in an LLC and had to fill out an "Authorized User Designation" form. Limited to two additional authorized users (who can also check in for Open Season reservations) so a total of three authorized users. I believe that HGVC treats non-individual forms of ownership identically (meaning that owning in a corporation or trust is handled the same by them). I was able to add the authorized users as an officer of the LLC, I would think that the trustee would be able to add authorized users on behalf of the trust. Club Support will send you the form.
One advantage of owning in an LLC (or trust, I assume) is that you can simply submit a new Authorized User Designation form if you want to change the individuals who are allowed access to your timeshare(s). Much easier than having to change the deed. And as an extra bonus, they don't charge for a Guest Certificate if it's owned in an LLC (or trust, I assume).