I just remembered that when my son (He's 45 now) would get poison ivy it would spread over almost his entire body. One thing that worked surprisingly well was a trip or two to the local high school indoor swimming pool. The cool water would help, of course, but the thing that would make the poison ivy disappear in a matter of days was the chlorine! It was almost hard to believe how well it worked, for him at least. And, Wizard, my wife does the hot water trick, and it works exactly as you stated
For some reason I don't get poison ivy... Sorry