No problems
I've never had a bearing wear, rust or fail when using bearing buddies on travel, utility, or boat trailers. The wheel bearings must be installed properly BEFORE the bearing buddy is applied. That means no air pockets in the structures at all. Packed solid before assembly and afterwards. It's a greasy, messy job to force grease in by hand, but necessary. You an do it wearing viny or latex gloves. Even preload the bearing buddy as much as possible before hammering into the hub. Heat, due to friction and/or braking will cause all greases to become more liquid and obey gravity, sinking to the bottom of the containing structure. Any air will rise to the top. When the hot grease and air cools, it creates a vacuum (boyle's law) which draws air in past seals on either side of the hub if possible. If the axle is underwater while it is being cooled it will draw in water past the seals. That is where most moisture comes from, especially if trailed a long ways and launched quickly. True of your tow vehicle's rear axles, too.The more frequently a bearing is used on the road and in the water, the more frequently the seals will need replacing. Some regular weekend fishermen might need it every year, some of us can go 10 years without a need. Anything rubber however will dry out and crack or shrink give time and ozone or UV exposure. So annual examination is required.