Not sure what you are used to but the sites in the three campgrounds we stayed at (Canyon, Madison, Bridge Bay) were all very short on space. They sure pile everybody in tight. Next time we go we will be staying at National Forest campgrounds near the NE or W entrances. We stayed in a popup w/o heat in July and woke to snow, frost and temps below freezing most nights in 2010. You can do it w/o heat as we did but we went to sleep clenching our sleeping bags hoping the nights went super fast.
If you have never been to Yellowstone be prepared to do lots of driving. Budget lots of time to get around and keep that daily list on the short side. Time flies. The roads are narrow and the speed limit is 45 and you will be driving slower than that most of the time too.
