I just came up the highway and virtually all of the Parks and RV parks have been nearly empty. We havnt made a reservations anywhere. Including such popular stops as Skagway...which by the Way DONT MISS and Valdez...even more scenic than Skagway.
While I see the number of RV's increasing slowly as we get towards June. I wouldnt worry.
I would make the trip as fast as you can at least until you enter the Yukon. But even as beautiful as the Yukon can be it pales in comparison to Alaska.
The drive is EASY. The road is good. Be prepared for incredibly high fuel prices in BC and some parts of the Yukon...needlessly high. Fuel is much cheaper once you get to Alaska.