If using a quality bulkhead, you won't have any problems. However, for an added sense of security, some people like to silicone around the edge of the bulkhead after it is installed.
Putting silicone in the hole, or around the edge of the hole before installing the bulkhead is not recommended and can actually cause more problems. Bulkheads come with gaskets, they are not designed to be used with any additional sealant.