It's been 43+ years since I last drove on the Alaska Highway. Each of the four trips was memorable, but they were in either May or July, so I can't say much about March. This was before anything was paved, so it was slow--we averaged 33 mph from Dawson Creek to the Alaska border on the first one--didn't keep track of the others, but we drove equally slowly. But by going slower, we had no mechanical issues at all. Others blew tires, slid off the road, etc.
We lost a windshield only once--baseball sized rock from an oncoming motorhome. I do recommend putting protective covers, either plastic or metal grid, over the headlights--you sure don't want to lose those if you're going to drive at all in the dark.
Fuel was available then about every 25 miles, and the only problem we ever ran into getting it was that it had to be hand-pumped at Mile 222, because the power was out. They had one of those old fashioned pumps, where you pump 10 gallons into a glass jar at the top of the pump using a long handle, and then it drains by gravity into your fuel tank--a little slow when you're getting 30 or 40 gallons.
Three of the trips were on the Alaska Highway. When we left Anchorage for good, we drove to Haines Junction, then to Haines, and put the motorhome on the ferry to Prince Rupert. We drove from there to Seattle, to where the car had been shipped. That ferry trip was well worth it--gorgeous scenery, very relaxing. The only disappointment was that it went through the night, so it's hard to see what you're missing in the dark. Some really fun memories about that trip!
Get a copy of the Milepost, which is available at any major bookstore or online. It's the bible of the Alaska Highway, and really helps to make it an adventure rather than just a drudge drive.
Good luck!
Cary