Trailer brakes as a whole are a nightmare!! Dunking metal parts into saltwater is never good, but a necessary evil.
If you spin the drum you should hear some noise. You want the shoes making some contact with the drum when properly adjusted. If you aren't in proper adjustment, the chucking feeling you get when start/stopping is annoying as hell.
I've already replaced my shoes twice in 3 years. Its the sitting in between trips that rusts them out.
Next year I'm going with new backing plates, hardware shoes and drums. We'll see how long that last!!!