We thought, due to the down economy, that last minute planning might be ok for an August trip to Yellowstone in our 25' Airstream trailer plus tow vehicle since we don't care if hookups are available - NOT. We were planning to stay about a week. All NPS campgrounds in the park that take reservations are pretty well booked. We wanted to avoid the commute in everyday from W Yellowstone or Gardiner, but I am researching options there now. I got 2 nights at West Thumb, that was the only thing open. We were hoping for Madison. Does anyone have experience with cancellations - how likely? Or first come first serve at this time of year? Of course I can try calling every morning to see what they've got. The problem seems to be all the sites can be reserved with only 2 day cancellation notice, so notice if any will be very late. Thanks for any assistance.