Several months ago, I replaced all the horizontal wiper seals (the ones on the top of the slides), as well as the top bulb seals, as they were all rotten from sun exposure. I ordered from the Trekwood site. I needed 36 feet of both, which gave me less than a foot over when I was done, for our four slides. For the slide seal, they have a screw through the rubber at each end, and after removing the screws, the flap just pulls off the metal it clips onto. The bulb seals were a little more involved, but it just took removing the corner plastic pieces at each end of the slide on top.
The wiper seal is:
http://www.trekwood.com/products.php?product_id=139553
The bulb seal is:
http://www.trekwood.com/products.php?product_id=139567
The cost of 36 feet of both, plus shipping was $215.43, and I think replacing both took not much more than two hours.