We bought our MH (used) in Boulder, CO in early spring, 2012 and took it to my brother's place in Vancouver where it sat until mid May. Then we flew down and the three of us drove it from Vancouver, WA to Anchorage, AK in 99 hours - basically driving around the clock, no toad, and nothing else much except something to make sandwiches out of.
The trip was good, with very little traffic. Because of little traffic, we found a lot of the places weren't open in the middle of the night to get fuel, so we stretched it awful thin sometimes. And due to lack of tourist trade early in the year, you won't find a lot of camp grounds open. Be sure to make some phone calls as part of your planning.
One night at Chetwynd we had to give it up at about midnight because it was snowing too hard. I had about two inches on the front of the MH and they had just paved the road so there weren't any reflective lines on it yet.
I'm not sure how you're defining "early spring" but considering that you're planning on taking all summer for the trip, if it snows, pull over and wait. The roads will usually clear up, but watch driving early in the morning or at late evening when the water on the road from the melting snow is frozen and slick.
I'd watch the weather rather closly in Sept. Moose hunting usually runs around Sept 1 - 20th and we almost always have snow, and sometimes it doesn't leave like with the spring snows. As you travel south from either Glennallen or Fbks, you're going to go up in elevation which means more snow that doesn't melt.
Bill
Nodwell RN110 out moose hunting. 4-53 Detroit, Clark 5 spd, 40" wide tracks, 10:00x20 tires, 16,000# capacity, 22,000# weight. You know the mud is getting deep when it's coming in the doors.