We've had several boat trailers over the years and always ran bearing buddies dust caps whils pumps grease inward and keeps the hub pressurized durring water submersion. Always used marine grade grease when I services the trailer bearings each year. I use the same grease on my TT and hit the EX lube fittings a little bit before a long trip.
*Currently trailer-less but shopping
07' GMC Envoy w/ P2 controller (current TV)
88' Chevy K5 Blazer (soon-to-be TV)
74' VW Superbeetle (1303)