Ugh, tried some dry graphite and some white lithium down the sides. That's not where the squeak is, so I took apart the door and lubricated the slides that go up and down - that's where the squeak is. Liberally sprayed them with lithium grease as well, tested it with everything apart, no squeak. Put everything back together, test it. Squeak returned... Maybe leaving it for a while will let everything soak and it won't squeak next time I roll it up.