I would use Highway 2. It is a great ride. Have done it numerous times east and west bound between the UP and Washington both in the current rig and when I pulled a 40' fifth. As it is, I have never made a cg reservation only because I don't plan on what days will be my travel days and what ones won't, and when a travel day what time I will start in the am and when I will quit. I also have never not found a good place to camp and I don't do Walmarts etc. I guess if I were to make reservations, it might be at Glacier and I'd probably go for a private cg. Plenty of them around and have used a number of them on both the east and west sides of Glacier. Many state park cgs keep some 'walk in' sites available and if you have a quitting time of 2 pm or so, you should get in. Also along the way many towns and counties have a town or county park with, usually FHU, a few camping sites - normally big sites. Use your smart phone campsite apps to find them. Gas and diesel fuel are plentiful along the way and most stations are kind of rural in nature with ample space to maneuver a big rig.
