I don't fish the Skagit at all, but on the Hoh, the bull trout seem to also hammer hardware with reckless abandon. I fish during the day and do not see why they wouldn't strike just as readily in low light conditions. Water conditions do not seem to deter them from striking, even if there is a lot of glacial runoff. They will hit surprisingly "large" spoons and spinners. As for flies, i'd probably use something that had some flashabou, silver tinsel, beadhead, eyes, etc.