I have a 2005 Itasca Suncruiser 38R.
Your ice maker water line shut off is located under the sink in the line that goes to the small drinking water faucet on the sink. I had to pull the line up from behind the back of the cabinet to access the shut off valve.
For the complete plumbing diagram for your 2004 Itasca see Winnebago's website.
Sarver, PA/Crystal River, FL/Shelocta, PA · FMCA 335149 · W3TLN
2005 Suncruiser 38R · W24, no chassis mods needed · 2013 Honda Accord EX-L · 2008 Honda Odyssey EX-L