I remember a large-space, RV-designed lot by some of the major thermal features but it was more than halfway filled with cars, too, since the car section of the lot was already completely full. (That was after Labor Day in September.)
It's good to get an early start every day before things get so crowded.
Xantera has some tours that leave from campgrounds (and other locations) and we took two - Circle of Fire was a good overview of the park, and another one left at late afternoon for wildlife viewing. Driving/parking was the bus driver's problem while we just hopped off and saw the sights.
ToursI don't love bus tours as a rule but those worked out pretty well for a first visit orientation to the park. Then we spent the rest of our week driving around to fill in the gaps.
It's worth downloading the Experience Planner brochure on that web page - tells about some free tours available, too, like one of the Old Faithful Inn.
