It depends on whether the first page of the trust contains all  the information they need to determine if you can vote in the election. Being the trustee itself is not automatically enough, since in the body of the trust, there could be restrictions on what the trust can own or on the trustee's authority to make decisions (e.g. vote) which may limit your right or discretion to vote, or even arguably impair the trust's ownership of the property. Therefore, they may have the right to see the entire thing, to make sure that you have the full authority you claim.