I went this year, left in May ... early May in fact. Many here said it was too early, and partly they were correct. A lot of the "mom 'n pop" campgrounds and gas stations were not yet open on the Alcan... some of them appeared to open in July and close in August (wtf is the point)
In May, there were very few RV'rs headed west / North, in fact most of the RV's I passed were headed the opposite way.
There is plenty of snow left in the mountains making them beautiful, and the inland lakes are all frozen so no fishing (and no fishing related crowds)
There was plenty of black bear, elk and eagles. Also saw some bison, goats, sheep, etc.
Some "unmaintained" roads will be closed by snow, mostly in the mountains leading to scenic places like the Salmon Glacier, Hatcher Pass and a few others.
Traveling through Canada, be mindful of Victoria Day (mid May, was May 18 this year) - there will be crowds at the campgrounds that are open.
As I returned mid-June, the snowbirds were returning to ALaska, giant Class A's towing trailers and / or cars behind them, all with Alaska plates. The organized caravans were also starting... when a caravan stops for fuel, prepare to wait hours for a pump, or find another station.
Edit: My equipment was a 20ft TT and a 1/2 Ram with the 350 Hemi
Edit #2: Cost .. A LOT, spent over $6k on fuel, round trip was 11,300 miles give or take. In populated Canada expect to pay $5-6/gallon for fuel, and in Northern Canada along the Alcan, make that $6-8/gallon
2013 KZ Sportsmen Classic 200, 20 ft TT
2020 RAM 1500, 5.7 4x4, 8 speed