We spent almost six weeks on each side of Glacier this summer, with a stay at Columbia Falls RV Park and the St. Mary KOA. We found Columbia Falls to be a great base on the west side as it is a small town about 15-20 minutes from the west entrance and has supermarkets and restaurants available. Kalispell is only about 15 minutes away and has about anything you could want available. Columbia Falls RV Park has great management and good monthly rates but not many amenities (pools, etc.) but does have a great WiFi.
The St. Mary KOA has a much higher monthly rate but they have a many amenities including pool, hot tub, etc. Our biggest problem at St. Mary was the smoke and the wind. Depending on the fires you may not have any smoke next year but I can about guarantee you will have lots of wind in St. Mary. St. Mary is about a 1,000 feet higher than the west side so is a few degrees cooler. That is one reason we wanted to stay there during Aug and Sept. Just be aware there is very little in St. Mary and the closest so-so supermarket is in Browning about 30 minutes away.
In between the two we spent five weeks in Alberta going to the Calgary Stampede, Banff, Jasper and Lake Louisa.
You can check out the blog in our signature if you would like to see what we did during the trip.