There's no need to pre-plan the trip to Alaska with a big rig. It's just like the lower 48 - there are campgrounds for small rigs and for big rigs.
You can even drive Top of the World Highway (not in the rain) and put your rig on the ferry at Dawson City. Semi trucks even get on that ferry.
Purchase Mike and Terri Church's book 'Alaskan Camping'. It includes Canada and the Yukon, also. It will tell you places for big rigs.
You'll see plenty of them on the trip. The RV parks are not like some in the lower 48. They are mainly just big gravel parking lots.
Relax, take the rig you have now, and enjoy the trip. You don't need reservations except for perhaps July 4 weekend and if staying in Denali Nat'l Park. We only made those about 3 weeks prior while we were traveling when we could better judge when we'd be there.