Icebox is the worst map.
I play Viper on Icebox, too. Here's what I'd do if I need to hold the entire map:
Definitely not a perfect setup but it gets the job done for the most part
She can't fully replace dome smokes but it's not uncommon to be running double controller, even in ranked (someone will often lock Omen or Clove). Her B wall is an incredible asset on defense and she can viably smoke everything off on attack (plus she has great lurk walls and lurk potential in general with mid)