Yes, you can! GradGuard offers renters insurance to students living both on-campus and off-campus! You will be able to select "off-campus" when you are going through the quote process at www.gradguard.com/renters. Then you will just proceed as normal and enter in your off-campus address as the insured address.
Your rental company or landlord does not need to be associated with the university for you to purchase a policy.