On our trip to Glacier and the Northwest a bit over a year ago, we stayed in Hungry Horse at the Mountain Meadows RV Park which moved near the top of our favorite campgrounds in our travels. It was a good base for us to visit Glacier and a pleasure to come back to each day.
We drove on to Spokane for our next overnight and then "skirted" Portland on our way to the Oregon Coast where we met RV friends and stayed in South Beach State Park.
I will share the route we took (but put it in reverse order, if I can) because that is the question raised by this thread. Leave I-90 at Montana 135 up to Montana 200. MT 28 to US 93 and on up to Hungry Horse. It was a pleasant drive pulling a 34' fifth-wheel.
I think I have that right. I know I could more easily trace the route as we took it, from Hungry Horse to Portland.
We stayed at the Riverside State Park in Spokane and then the next night at Memaloose State Park in Oregon just beside the freeway. These, too, were great places to stay.
What great memories we have of Glacier, Washington, and Oregon!
