I also have a 2008 Bighorn that I fulltime in. I measured the slide seals, and even bought longer flap ones. The best prices I found on the internet were for AP brand seals through a vendor on Walmart.com The other big surprise was that I ordered the seals on a weekday afternoon, was at a park in a fairly remote area East of San Diego in the mountains, and had the seals delivered the next day at noon (with no expedited delivery).
I bought these 2 items:
https://www.walmart.com/ip/AP-Produ...V-Slide-Out-System-with-2-7-8-Wiper/135387895
https://www.walmart.com/ip/AP-Products-1-x-15-16-x-35-Premium-D-Seal-RV-Slide-Out-System/108086694
Be sure that when you park that your side-to-side levelling is spot on. The slide rooms are designed to lean away from the main RV body a little (and old name for slideout rooms was "tip-outs") to help rainwater sheet away from the seals areas.
ON EDIT: While I was searching my Walmart.com website account I WAS ASTOUNDED to find EVERYTHING I HAVE BOUGHT IN WALMART STORES (MAINLY FOOD ITEMS) FOR THE PAST FEW YEARS DOCUMENTED ON THE WALMART.COM WEBSITE !!!!! I don't login with Walmart.com when I checkout in the stores, but I DO use my debit card routinely. The Walmart computer system must have linked my debit card to my purchase history online.