We went to Glacier for the 4th of July, and were disappointed that the GTTS road was closed. I must say that we stayed on the EAST side of the park & loved it immensely. There are a LOT LESS crowds there, and more to do.
We flew - so we didn't get to camp, but we would love to go back with our camper. The only problem is that it would take close to a week to get there from the Gulf Coast.
We would absolutely LOVE to make a trip that includes the Grand Tetons, Yellsowstone, Glacier, Lake Louise, and Jasper. They are all pretty much in a continuous line.
Of course once we got there we would have to sell the camper & truck, and then fly home.........
I'd definitely choose August/September over May.