The technique I've used for the past couple years is to cover the bits of the miniature most likely to chip or wear (exposed limbs, weapons, shields, heads) with a layer of Games Workshop Hard Coat. Then I spray them down with one or two light coats of Testors Dullcote. As long as I apply it sparingly (and generally indoors), I haven't had a problem with frosting. This method has served me well and my minis seem pretty durable.
One frustration I have with Testors Dullcote is that it seems to come in different packages. I've seen it labelled "Clear Coat Spray Lacquer" (with the product code "1260 Dullcote") and also labeled "Testors Spray Enamel" (also with the product code "1260 Dullcote'). As far as I can tell, these are the same product. At least I have had the same effect with both. If anyone else can clarify this issue, I'd be all ears.