Bear with me.
When I bought my ice fishing shanty I took it out for a test run in about 0 degree temps. I sat inside, with the propane lantern running and my breath condensing. Propane gives off water vapor as well. I noticed a large frost buildup on the ceiling and thought nothing of it.
Around 10:00pm, I went to leave, and found the metal zippers frozen shut. I could not get out. I looked out the windows and saw the cottage lights on shore going out one by one. I started wondering if I was going to have to cut my way out of my brand new shelter. I ended up taking the metal lid off the lantern, heating it up, touching to the zipper, melt the frost, inch the zipper, repeat, until I got out.
Went home and looked up "Frozen zipper on ice tent" and found links to ZIPPER WAX. Apparently that's common knowledge to those that have ever had a zipper freeze shut.
It comes in stick form. You apply it like a crayon. I'd guess that it would work if applied to the metal surfaces that your rubber seal is sealing against if that's the case. It's lasted me a few years between applications on my zipper.
It might work for you, it might not, but it might be worth a try to just take an old candle and rub down the metal where your rubber seal hits and see if that does anything.
Good luck.