Bill's right. In most states in the north, it's illegal to drive a vehicle without first clearing the roof. They've been cracking down on the truckers around here. Seems like every day in the winter there's a dash cam video of someone's windshield getting smashed as the trailers go under an overpass and wipe the top clean.
The bigger truck outfits are putting scrapers in the yard.
On topic: Adco covers are junk. We stopped carrying them mostly because of the warranty hassles. We now carry Classic, but I'm not sure they have a roof only cover.