We absolutely love Coulter Bay campground in the Grand Tetons. I think we could park there for the whole summer and be perfectly happy. Not huge fans of Yellowstone due to the crowds but if we go it is early in the season or after Labor Day. At Glacier NP you might try Mountain Meadow RV park in Deadhorse MT. We liked it but it wasn't in the park. I will strongly recommend that you take the Red Bus tour up the Going to the Sun Road. It is something you will never forget and the restored 1930's vintage buses are very cool.
John & Lisa