StressSolutions said, "...I suspect that you could use some of the sex lubes, too."
The KY Brand "Warming Ultra Gel" may be particularly valuable in this instance, and not just for its lubricity. However, I doubt it gets warm enough to prevent freezing.
In all seriousness, most modern car's door seals are not rubber as we think of it anymore. They are made from EPDM, which lasts much longer. The product I recommend (and use) is 303 Protectant. They have some nice info on EPDM and rubber on their site, 303products.com . And 303 lasts a long time on door seals if applied and allowed to penetrate (I'm going on 2 years). I even spent 3 weeks in Ohio over Christmas with freezing, wet weather, and my doors didn't even think of freezing shut.
303 is also the best product I've used to prevent sun damage to all of your vinyl and rubber. And it leaves about as matte a finish as you can get on your dash so it doesn't create dangerous glare (if you like the "bling-bling" shine, this won't give it to you).
Only problem with 303 is finding a local distibutor. Most RV centers carry it, as 303 products are popular with them because of its protection and durability on stored RV's. Their site should also have a locator, and you may still be able to get free samples that would be enough for door weather strips.
One tip with 303 is that a little goes a long way. And buffing it after it has set for ten minutes actually "sets" it in, resulting in even better durability.
Hope this helps (and no, I don't work for 303, I enjoy using their products).
Dave