I stayed at the whitefish RV park just last week. It's right in the town of whitefish, and it was excellent. Level site, lots of trees, reasonable price, everyone was friendly, clean bathrooms with lots of hot water, right next to the army and navy store in case you forget anything. 5 minute walk from a 24 hour grocery store.
The only problem was that there were no firepits, and our site was in the farthest corner of the park, so the wifi was kinda slow. I assume it's better closer to the buildings. Check their website below and give em a call if you want. I'm sure I'll be staying there again.
St Mary's, east glacier, and west glacier are also really nice, though the're more remote and have less services, so be prepared.
The one place that really struck me as beautiful was the campground in Apgar, near West Glacier, right on MacDonald lake. Although I haven't stayed there, we passed through last weekend, and it looked amazing. Apparently it's usually full, so you have to book well in advance.
If you're all about shopping in Kalispell, and less about the sights in G.N.P., the Whitefish RV park is an excellent base. Make sure you stop at the Barbeque shack for a pulled pork sandwich, and the city beach is worth a stop. The water isn't as cold as you'd expect it to be.
There are also really nice places along Flathead lake, which is pretty close to Kalispell.