Your best bet is to try to match what you currently have on it. You should have the round rubber ones on the slide itself as well as the :flapper" style on the bottom and the side and top that is attached to the RV.
I subscribe to Motorhome magazine. In the back, there is an ad for something called STEELE RUBBER PRODUCTS. They can match your seals to factory specs. Their website is https://rv.steelerubber.com/ phone number is 800-650-5137. it's what they do!
I had to replace my D-seal last year (on my 2012 Denali). Here's what worked for me. https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
This is the part that slides over the rail. The wiper portion is part of the rail but the wiper was still in good shape on my rig.
I appreciate all the replies and help. DH called PPL and they sent pictures of what they have in stock. He was able to match up (at least I hope so... LOL) the pattern. I was shocked at the overall cost!
Wish us luck on installing them!
Linda & Van Hagan
2013 Denali 285 RLX 5th Wheel
2015 Dodge 3500 DW Mega Cab