We spent 2 1/2 months to Alaska and back last summer (2016). We left ND in late June and had reservations over July 1-4 in Alberta (July 1 is Canada Day). We only made reservations a day in advance so we could get into preferred campgrounds. We stayed in a mix of primitive public and full-hook-up commercial campgrounds.
We missed staying in Denali (Tek) as there were no larger sites available when we looked at reservations a week or so in advance. If (when) we go again I would project out in advance and pick a week for Teklanika then just adjust our travels to accommodate.