We've done this route many times with our 40'. 89 through Flagstaff to 89A south of Page where 89 continues to Page. 89 is presently closed so 89A over to Jacob Lake/Fredonia is the way to go.
As mentioned above, stay on 89 and you can easily work in Bryce Nat'l Park. We try to stay off interstates so we take 89 through Utah to Heber City. We then get on I-80 east to Evanston and pick up 16/30 to Montpelier and then pick up 89 again to Jackson, WY (Grand Teton Nat'l Park) and continue north to Yellowstone.
Your best bet for refueling before the Tetons is on 89 from Alpine to Hoback Junction. In Thayne there's an easy access Maverick station on the right with good prices. Just before entering Jackson there will be 2 major groceries and a liquor store if you need them. On the left is Smiths Plaza which also has fuel but not easy access with the MH. A little further north on the right is Albertsons. West Yellostone's groceries are very small but usually you can find normal items. West Yellowstone also has expensive fuel.
Try to get into Colter Bay RV for the Tetons for the best experience if you need hookups. Otherwise Gros Ventre or Colter Bay campground (next door to the RV park) are doable with a 40' but it's dry camping and no reservations but they each have 300 sites. We've always gotten a site.
Yellowstone: Fishing Bridge is the only full hookup. We've stayed at Bridge Bay, Madison, and Mammoth.
Out of Yellowstone to Glacier - depends which side of Glacier you want to stay. There are many nice routes. We have continued on 89 to East Glacier. Or for West Glacier you can take 287 to I-90 west to 93 at Missoula. There are also others depending on what you want to see. I think we've taken all the roads in that area with no problems. 191 out of Yellowstone is also good.
If you have time, you might want to purchase the Mountain Directory - West (online) which gives you detailed info about any questionable highway. We use it all the time. Have a great trip!
