I saw some big motorhomes going real slow (5 mph) on the frost heaves near Destruction Bay. You'll feel it if you don't. Also, the Hwy from Tok to Glenallen has some bad potholes. The Milepost will list the bad sections. I got my windshield cracked coming back on a gravel stretch north of Ft. Nelson, though it was cracked when I went up, couldn't see any point in replacing it until I got back.
Be sure to get some Canadian cash for your trip, as it will save you from having to go inside and wait at some of the smaller gas stations if you can just hand the guy cash, like at Coal Creek. I got $1,000 and had plenty for food and gas both ways, but I was driving an SUV.
Don't get compulsive to get there, take your time and enjoy it. Lots of beauty and wildlife.
Search on Island Girl Walkabout for a really nice blog about the trip, taken by a couple in a big rig and pulling a car. Nice photos, too.