We get these posts each winter. :? To keep it from happening you need to pull the carpet card off the tailgagte and lube up the actuator rods and latches. Same with our door locks, door latches and handle pulls. If things are already frozen up find an underground parking garage for a day or buy a buddy a 6 pack to use his garage. Scotty's trick worked for me the first time mine froze up, but things weren't nearly as cold as they are right now.
i got a really nice jar of mobil 1 synthetic all-purpose auto grease at autozone and have never looked back. the latches, door straps, and sunroof hinges/rails absolutely love it. holds up nicely in winter. i don't even use a gun. i just smear a coat on when needed with my fingertip and i'm good for like 6 mos. on all of them. i've also been known to give the door handles a light spritz of wd40 to keep them smooth when they like to snag at that last 1/8". then they close all the way on their own.