We did both the east and west side. On the west side, there is the KOA and several others including Glacier. There are the ones inside the park (none of which have hookups). There is also an 18 hole golf course just outside the west gate in West Glacier that has some sites right next to the clubhouse. You won't find that one listed in any of the books. I think you need to call the golf course for info about them. Neat golf course by the way. Last time we played there had a moose trot across the fairway in front of us. Spend a few days there and take the Red Bus up to the top of Going to the Sun Highway. (Don't do the round trip down to the east side. Do that on your own when you stay on the east side. (More about that later.) Lots of hikes to take in the park and check out the Lodge. Outside, spend some time checking out the area. Kalispell is a neat town and here is a wonderful winery on US93 on the west side of flathead lake. Ride over to Whitefish and take in the downtown farmer's/craft market at the train station and then take a ride up the tram at the ski slope and hike back down after having a Moose Drool and a bite to eat at top.
When you get done on the west side, take Highway 2 and head east along the south end of the park. Stop at Nimrod and check out the railroad yard and lodge. Lots of old railroad stuff and a pretty good restaurant...also have several cottages for rent that are converted cabooses. Further east, stop and check out the gorgeous lodge at East Glacier Park (or do that on a day trip out of St Mary). After East Glacier, head to St Mary but don't take 49 (Looking Glass Hill Road) with your rig...save that for the toad or the tow vehicle. Instead, continue on US2 to Browning and take US 89 to St Mary. In Browning at the intersection of US2 and US89, you will find the Blackfeet Indian Museum. Worth a stop there. Continue on to St Mary on the east side of the park and stay at either the KOA or Johnson's. They are pretty much right across the street from each other. Johnson's is on a hill and has a great view plus a good restaurant. From St Mary, take the toad or tow vehicle and drive west up the Going to the Sun to the top. Park up there at the Logan Pass Visitor Center and take the hike up the hill. (If you take the Red Bus round trip you won't have time to do the hike.) After that, take a day to drive up to Babb and go in to the Many Glacier park entrance and drive up Many Glacier Road up to the lodge. There are several hikes you can take there but an easy, short one goes from the lodge around the small lake. This is a beautiful area of Glacier Park and not many people make it here. Kinda like the difference between the north and south rims of the Grand Canyon.
If you still have time, take 89 north of Babb to 17 thru the park to the Canadian side. (17 turns to 6 in Canada.) Beautiful drive and easily done with the RV. Press on over to Waterton Park and take in the Canadian part of Glacier called Waterton Lakes National Park. There is a really nice lodge there and a little town that has a campground with 238 sites, 95 of which have full hookups.
Got more time? Head up the Cowboy Highway to Banff and then to Jasper. All I can say about that is WOW! ;D