Theory crafting another lightning arrow build, but it freezes

I currently try to get my mapper running but I'm not sure where to go from here. I went with lightning arrow since it felt pretty good till now.

I currently try go get a twist on it since magnetic salvo got nerved. I picked up whispers of the brotherhood. It felt pretty easy to freeze enemies and now I want to combine it with sth like cast on freeze... But I struggle to add skills to it due to mana cost. Do you guys got any advice?