Hopefully the Going to the Sun road will be open by July. Varies depending of snowfall. To fully to enjoy the Park you need to spend several days on each side. Personally, I like the East side best. The area around the West entrance is crowded.
There is a KOA in St. Mary's on the East side.
Staying on the East side you have the opportunity to visit the Waterton Park in Canada. Then on the east side be sure to visit Many Glacier and Two Medicine.
Drive up to Logan Pass from the east or west and hike out to Hidden Lake.
Scroll thru the "Travel Photos" link in my sig. We were there last July.