We used the nice Provincial Parks, Yukon parks and beautiful boondocking spots. We didn't make reservations but we like to pull in early in the day. Convert some cash when you enter Canada because many of these only have a dropbox for payment.
The only reservation you really need to make is for Denali's Teklanika campground (highly recommended) which is the farthest one you can drive your RV. We stayed 5 nights and only made the reservation a couple weeks prior to arrival when we could better judge when we'd get in the area.
As it turned out, we got nearby a little earlier so on a whim we boondocked outside the park the previous night at a lovely spot just outside Talkeetna. Then early morning we drove into Denali and easily secured a spot in the front campground - Riley Creek for another 5 nights with our 40' motorhome.
Spending 10 nights in the park we saw every one of the major animals of the park; some more than once. We also say 'THE' mountain 7 of 10 days. Awesome!
There are plenty of fuel stations however you really need to drive on the top half of your tank just in case the next one is closed. Since you're leaving late in the season, some do close down when fuel is empty.
I would also suggest purchasing Mike & Terri Church's book 'Alaskan Camping' which includes Canada and the Yukon. It gives RV parks, public parks and boondocking spots. Don't rely on 'The Milepost' for finding these kinds of spots. The Milepost is a good read for history and maps.
Plan to drive up on the Alaskan Highway and return on the Cassier Highway. Stop at Hyder and you'll be at a good time to see the bears fishing.
Hope the fire issue slows down for you! Have a great trip!
Full-Timed for 16 Years
.... Back in S&B Again
Traveled 8 yr in a 40' 2004 Newmar Dutch Star Motorhome
& 8 yr in a 33' Travel Supreme 5th Wheel