Wow! I really don't think you should make reservations for the whole trip. You never know what the road conditions will be and any fire delays. You also might want to spend more time in one place and less in others.
You can always find a place for a night and the wonderful boondocking spots are awesome.
The only reservations I'd advise is for the July 4 weekend and for staying IN Denali Nat'l Park. For those we only made them about 3 weeks prior when we could better judge where we'd be.
As it turned out we got into the Denali area earlier so on a whim we boondocked nearby and drove into the park around 9am the next morning and easily secured a spot for our 40' motorhome for 5 nights at Riley Creek campground. After that we moved to our reservation spot at Teklanika campground, the farthest you can drive the RV.