My OEM Firestones on my Ram lasted about 20K, they were horrible. OP, I would pay attention at campgrounds to trucks like yours and see what tires look appealing to you and talk to the owner of the truck. Its my experience that most campers are willing to discuss pros and cons of their trucks/campers/equipment to other campers.
My FIL has a GM and has some really nice Goodyears on his truck. I wanted the same for my Ram, but they didn't make them in my size. I was able to find several HD Ram owners that recommended the Nitto Duratrac (I think...) that I ended up buying. Same truck, same general climate, same general conditions. That's my suggestion.
Either way, buy a NAME BRAND. Buy a tire you've heard of before. Buy a tire that is priced appropriately (for an HD truck tire, $200-250 per tire is probably about an average price). If you find tires that are super cheap... be cautious. If you see prices that are insane... be cautious.