Shower Surround Sealant

I'm replacing the shower faucet. It's mounted on what amounts to a plastic box. The plastic box is surface mounted to the shower surround with screws. The joint around the box is sealed with some clear sealant. To remove the box and gain access to the mounting nuts on the faucet I have to remove the box. Then I have to re-seal the joint around the box. That joint is currently sealed with some clear sealant. The question is, what should I replace that sealant with?