Sure. the trailers are made to have the back axle dunked. however,
there is always going to be water seeping into the wheel berings even
though the trailer may be brand new, and the wheel seals in new shape.
The seals are made to keep the grease in the bering, but not
necessarily anything else out.

every year when you winterize your boat and park it, you should pull
the wheel hubs and have the berings flushed out and new grease
installed. that's part of winter maintenence.

after I do this, I even go as far as parking the boat and trailer,
jacking it up and putting it on wheel stands so there is no weight on
the tires or springs. trailer stuff seems to last longer