I once found myself on an unplanned 13 hour ride, and I haven't forgotten it to this day. We were scouting/hunting Bears in Idaho (first day of the hunt) and wound up going a lot further than planned. All of the snow hadn't melted, so sometimes we were on solid ground or mud; other times we were in 2-3 feet of snow. My biggest problem wasn't saddle sores, it was my knee's. On occasion we would dismount for a rest and I could barely walk for the first 5 minutes. I had my stirrups adjusted too short. Only after that first day did I realize that my knee's wouldn't hurt so bad if I adjusted them to full length for my legs. The front half of my foot kept good contact with the stirrups, and I could raise up in the saddle on my tip toes. Damn my knee's hurt just thinking about it.
Since it was still chilly, I was wearing my light, insulated underwear, and did not suffer any saddle sores, although my ass got numb on several occasions, thus the dismounting for short breaks. Hopefully, some of the Horsemen that visit this forum will give both of us some savvy advice. Good luck on your trip. Sounds like it's going to be a great hunt. Good hunting, grayghost