One of the first things I did beside washing was to use rubber protection on all rubber trim door, hood gaskets. The car sits outside. No usable garage. In northern NJ I have friends who always complain about frozen doors in winter. When I use Gummi Pfledge rubber protection the doors never stick or dry out over time and the rubber stays elastic. My old car with 210,000 never had a problem outside. The only problem I notice is that it does attract dust easy. The BMW guys really love this stuff on the forum I found it on. By the way the skinny rubber strip between the lower hatch glass and the car body seemed very gray and dry (take a look) until I applied this stuff. Now it's black and soft again. Oh by the way I also use 303 protectant but this stuff last longer for outside IMO. Clay bar and waxing is next as soon as the weather gets above 50deg.
I used Einszett Gummi Pfledge on the door seals of my last car (BMW 545i) to alleviate a well-know squeaking issue on those cars. 303 Protectant is also great--have used it on tire sidewalls and other exterior rubber for a long time.
+1 on the 303 and it can be used for other applications around the house too. I have a new front door made of some type of plastic that has the appearance of wood in both color and grain. I use 303 to protect it from direct afternoon sun.
One thing to do periodically with the gasket around the hatch opening: starting at the top/centre, pull it up and off the lip (it's just attached by friction) and have a look under. If you get any amount of rain you'll likely find some slimey grunge under there.