Thank you both very much for pointing me in the right direction. I tested your suggestions and it worked using the outside (normal) lever of the tailgate. And to clarify, I have an over sized ski storage box on the roof of my car which blocks fully opening the tailgate, but still needed access to the rear compartment. So I won't be driving with the liftgate open so the poisonous gas warning does not apply.
This is my first post on the forum and I really appreciate your assistance!