It has been a couple of years since I was there but I remember in June it was cool. I have heard that they have snow up to June. I believe that the bathrooms in the RV park are not heated. The showers in the tenting area where the laundry is located is heated. You will be beating the crowds and should be able to have all the time you need to talk to the Rangers, and be sure to do that as they have wonderful stories on the history of the park and area. Check the park calendar for events in that time period.