Been to AK twice in 2013, 2014. Roads are paved all the way on AK Highway and most of the way on the "Top of the World" and the Canadian "Cassiar Highway." The only gravel is the ever on-going construction/repairs as well as frost heaves and potholes. Most potholes, frost heaves are marked by flags or cones, but you can also spot them by oil marks and tire scrapes in time to slow down. You shouldn't be going more than 55mph anyway, even if that fancy sports car passed you with the top down. I passed him later while he was backing up to retrieve luggage that flew out of back seat. In construction areas, you should't go over 25mph no matter how smooth it seems.
As to mud flaps, I am slowly realizing that they do more harm than good, because when bouncing along (the recommended 4" clearance) isn't enough, because the flap strikes the ground and kicks up rocks onto the toad. I've tried home-built plexiglas shield, and all it does is bounce the rocks into the back of the motorhome and then bounce again over the shield onto the window, etc. I've tried the spray on shield, both the military spec paint (aircraft) and Rustoleum, but when it gets hot, it cooks it on and hard to get off. Looks awful when wet too! Ditto too, to the tape like shield sold by Camping World. This next summer, I am removing the mud flaps and will install the Guardian Shield as well as the Defender Apron for our return trip to AK. I found that a home-made apron made out of greenhouse cloth worked very well with bungee cords, but it didn't look neat after it got loaded down with mud and wear and didn't have the retractable features of the Defender. The only thing I don't like about the Guardian, is that it has to be removed for the toad to be driven... headlights don't shine through the solid material, and if the temperature is warm, you will have issues with vehicle cooling.
I expect though, with using both the Guardian and Defender in tandem, no more rocks should be thrown over the screen or barrier onto my toad, except for the oncoming vehicles throwing rocks at you.
Don't let the horror stories stop you, it is a trip well worth taking. And by the way, just north of Watson Lake (10 miles approx) take the Cassiar Highway about an hours drive to Boya Lake Provincial Park and stop for the night. It is a gem that you won't want to miss!