I know a guy that used his float tube on the Lower Skagit below Mount Vernon. He was fishing for pinks last September. He did fine floating down the slow main current' being able to kick he would slow his progress down river. He then would hitch a ride back up on a back eddy kicking again to go faster. He did this for a few holes down the river. But then again this was the deep, slow, lower Skagit and not the free flowing, fast, boulder garden of say the Sky or Sol Duc.