How do Huck and Jim avoid being seen while they are floating down the river?

Mainly, Huck and Jim avoid being seen by travelling at night, and then tying up the raft and sleeping during the day.  Twain writes some  beautiful descriptions of the night sky and travelling that way. When they meet up with the King and Duke, this easy way of life becomes more complicated, and then they have to make up elaborate stories (e.g., traveling with a "sick Arab") in order to go down the river in daylight.