Old Biscuit nailed it. The main seals are on the interior and exterior flanges of the slide. From my limited experience, and I guess it depends on manufacturer's design, the rubber wipe seal flips out when the slides goes out and flips back in as the slide comes in.
Probably doesn't make much difference but it makes me feel a little better that the wipe is an out'e when the slide is extended.
03 Itasca Sunova, Workhorse P32 with the 8.1 and 4L85-E