The west side of the park is quite different from the east. The west is more classic forested terrain with lakes. The east side has the rugged mountains and the glaciers, but also a lot of lakes. The approach to the west is easy, and even on the east side, the elevation at the east entrance is only about 5,400 ft, so you're not driving through a bunch of mountain passes to get there. You can't cross from one side to the other in an RV, since there's a 21' limit on that road.
The biggest campground in the park is at the western entrance. It called Apgar and is first-come-first-served. There are a lot of pull through spaces in that campground and it's a nice wooded area, but no hookups. Just outside the west entrance, you'll find the Glacier Campground. Also a nice wooded area, but with hookups. A mix of tents and RV's. It takes about the same amount of time to drive to the west or east entrances (about 19 hrs from the bay area), but there are more RV park options on the west side, for sure. Only 3-4 that I know of within an hour of the east entrance. There's lots of shuttle buses that you can jump on from the west to see the east side of the park as a day trip, so even if you stay on the west side, you can experience the other side of the park.
Don't know how long you plan to be there, but one other consideration is that if you stay on the east side, you can hop in your car and drive up across the border to Waterton Park, which is the Canadian side of Glacier. It's only about 35-40 miles from the east entrance to get there and I've been told it's even prettier than Glacier with a lot of wildlife. A nice day trip. Enjoy!