We did it twice in 2006, Mid-June and early October in a 28' Class C. Of course a car would have been easier, but we have had very few problems stopping at any of the view points that we wanted to see in mid-June, and no problem at all in October. There were several times when I let the passengers out, and circled around once or twice until I could find a spot to park. It would help if passenger cars did not use the larger RV spaces in the smaller parking lots.
We also do a lot of hiking and try to travel to less visitied areas. We do leave our CG early in the morning before most of the crowds, and also see more wildlife at that time of day. Talk to the Rangers and get suggestions for areas to avoid the masses.
We are leaving for Yellowstone in 10 days, and do not plan to get a rental car. You should be fine in late May/early June, and the MH will come in handy to get warm in after walks to the view points at that time of year.
As long as you plan to go off-peak season, you should be fine. We were there the end of June- first of July and there were lots of nearly full parking areas.
We watched one poor fellow towing a fifth wheel in the Black Sand Basin lot get totally stuck as he tried to make the loop at the end of the parking lot.
Ken & Kathy
Stella(the dog who now belongs to our neighbor )& Ruben(the cat)& Tiadora (nother cat)
2003 Chev 3500 D/A Dually
2002 Jayco Eagle 300fss TT
You can go in just motorhome, We see many rented ones there of all size and shape. You won't have to many places you can't go a lot of the drives are one way roads and most parking areas have room. You will be there before the traffic gets real bad so parking at turnouts and at the popular attractions shouldn't be hard at all. We pull our fifth wheel through the park from the south to Indian Creek 3 times a year and have always been able to stop along the way if we wanted to. I can only think of 2 places the petrified tree drive and the sheep eaters cliff drive that you may not be able to go.
hope this helps
Him and Me
06 Dodge drw
06 Crossroads Zinger (searching for our dream fw)