I seal my bulkhead connections with silicon. That said, the power leads are pigtails that terminate with spade connectors. These are covered by waterproof fuse holder covers made by Ancor. These can be filled with di-electric grease. Available at most large marine supply stores( West marine etc.)
Liquid tape, as noted in previos posts, work great too, easy to apply, easy to remove. Takes a while to build up, but that's what winter is for.