You can only wavedash OOS to counterattack if Marth uses a laggy move - f smash is really the only move safe to punish on block. All Marth really needs is a lot of fairs, dtilt and CC and Climbers get ****ed up.
As far as camping goes, Icies don't have anything reliable enough to play a campy game, ice bricks have too much ending lag to be safe. The blizzard can be put to good use, as its IC's only move to outrange Marth, but it has its limitations aswell, depending on how Marth reacts.
Anyways, I know a lot about the MU which is really the only reason I manage to get by, but it's tough, very tough indeed.