One of my brothers moved up there in 2005 and blew all 4 tires on his trailer, my other brother who lived up there moved down to the lower 48 this January and blew out 2 of his trailer tires.
Not to be a jerk or smart*****, but just how fast do your brothers drive and do they overload their trailers?
I've personally driven the Alaska Highway at least 15 times and I've never had a flat tire on any of my vehicles, nor have I ever heard of anyone blowing all 4 tires on one trip. In the 70s when the roads were all gravel you would often hear of people blowing tires when they hit the sharp metal pieces left by the graders, but that hasn't been a problem on the the Alaska Highway for 20+ years.
Make sure that all your tires, especially your spare, are in good shape, properly inflated, and not overloaded. While there are plenty of places to get fuel there are streches on the highway that you can go 400-500 miles between places that have a good selection of tires. The Alaska Highway is not the place to take a vehicle that isn't maintained properly, not because the road is that bad of shape, but because the distances involved between major centres can be quite large. If you break down in Whitehorse you will have a good dealer to work with, 500 miles either side of Whitehorse you aren't going to find a Dodge dealer, let alone a good one.
Oh, and slow down, if you drive at 70 you will get more rock chips (remember the faster you are moving, the faster the rocks hit you), you will shake your vehicle appart, and eventually you will break something. I've talked to two people who have driven the highway at the same time, one said it was terrible, the other said it was great, the difference, how fast they drove.
Paul