There are a couple routes:
I-15 to I-90, MT141/200/83/2 to Apgar, MT and Glacier NP - 990 miles
NV93 to I-84 to Boise, ID, 55/95/12/I-90 at Missoula, MT then 93/35/2 to Glacier .... a very scenic route over an interstate but approx 200 mi farther.
As far as where to stay and do it's hard for someone else to make suggestions. It depends how far you want to drive each day, if you want to stay at places longer than overnight, what kinds of things you like to do, etc.
You could create a route on Google Maps and then zero in on it to see what's around and what interests you.
The same for places to stay. There are plenty of RV parks, public parks to stay. . just depends where you want to stop. There are good RV park review sites out there such as Campendium, RVLifeReviews, etc. Just plug in a town where you think you may stop or get tired of driving and then see what's around there.
All national parks have an excellent web site with information on camping, special alerts, road issues, things to do, etc. Scour it thoroughly & especially right before your trip to see if there are any kind of closures or road construction going on.
https://www.nps.gov/glac/index.htm
You won't be able to take the RV across the Going To The Sun Hwy within the park so you'll have to drive your vehicle or the trolley or there's even a tour company that uses old, spiffy small buses.
https://www.recreation.gov/timed-ent...icket/10087087
https://www.nps.gov/glac/planyourvisit/guidedtours.htm
There are campgrounds in the park itself and some just outside the park. Other than the east side, Apgar, entrance there's also a west entrance at St. Mary's. Apgar has a lot more campgrounds, restaurants, shopping and more people. If you choose St. Mary's you may want to re-route a different way to take you closer to the west side.
Things have changed the past couple years and you'll need reservations for many things that were never required in the past so some planning will be needed. Make reservations as early as you can. I'd advise to first get your park reservations and campground reservation and then plan your trip up there with the amount of time you'll have. If you stop early in the day around 3pm or so you'll get campground spots without reservations or when you think you'll be ready to stop driving and hour or two from a point you can gauge where that will take you and call ahead for a reservation. Have several options in mind.
Do a Search on this site (top of page) & you'll find lots of other posts on the subject.
Have fun planning!
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