We were out for 7 weeks this past winter and only 5 nights in a campground..(2 in Quartzite) and that week in Off-Pavemnt's back-yard outside of DV.
From my travels, there are some spots just west of Cody..and south towards Jackson Hole. And yes, the western approaches to Yellowstone. I think I can cram into the parking area at the hot springs just out of Mammouth campground, too.
We aren't out with a destination in mind...although I recall a fine distillery just west of Yellowstone...I may need to find that again.
Gary