I had this problem, so I though other people would like to hear about my solution.

I continue to have leakage problems even with the grommets and sealing them with silicon. The silicon has a week bond and is easily broken when flexed, so silicon wasn't a good option for sealing it.

Polyeurethane sealant, on the other hand works great! I used Vulcem 116. It takes 3-4 days to set up enough for you to use it, but it's worth it. First off, it reacts with water to cure, so it likes being submerged after it's set. Second, it's got great strength and flexibility, and third it's great at holding water back. It'll cost just under $5 at most hardware/home improvment stores.