As a Dual Squelcher user, I like throwing Splat Bombs at the Rainmaker if the enemy team gets the shield explosion to see if I can catch anyone out. They're also great for getting multiple kills when your enemy is crowded around the shield, and they're a great pressuring tool for the enemy Rainmaker carrier.
I tend to use Bomb Range up, Ink Recovery Up, Ink Saver main, Cold Blooded, Ink Resistance and Swim Speed up in this mode as a Squelcher. It keeps my battlefield capabilities versatile so I can fill the role of aggressor, support, or Rainmaker carrier effectively.