Last time that I was there it was mid October and we stayed at a Private RV Campground just outside the North Entrance ( it was just before the bridge that goes over the river into the town of Gardiner) of YNP the campground was right on the river, and had full hook ups and we had a newspaper on our doorstep every morning! We couldn't stay at Mammoth Hot Springs because it was full in mid October. I suggest the North end of the Park due to there is more animals in the North end. On our last trip we drove in from I-90 Livingston, Mt. then to Hwy. #89 into Wyoming. All the elk were herded up at the Mammoth Ranger Station and the Bull Elk were fighting over the Cows. We also took the Yellowstone Loop Drive in our car it starts at Mammoth goes due south near Mt. Holmes, then east to Canyon, then north to Tower Junction then west back to Mammoth. You can get everything you need (supplies, gas etc.) in Gardiner. We must of seen 500 deer between Livingston and Gardiner big herds in just about every farm field. I've come in and out every entrance and my two favorites are Gardiner & Cody! In mid October it snowed in the high country every night and the YNP Road crew had all the roads plowed before daylight I was surprised to see the Bison dragging there bellies in the snow between Mammoth and Mt. Holmes in the high country. During the day in mid October it was in the high 60's to low 70's. Have Fun!