Re: right way to fix
The trailer is either steel or aluminum.
If it is rusting it is steel.
Galvanized means the steel is coated with zinc instead of paint.
Galvanized is the preferred coating, especially for salt water.
But you still need to inspect the interior or the frame tubes.
In as much as you are within 25 miles of the ocean; This trailer has likely seen a lot of salt water.
If the previous (and current) owners were not religious about rinsing the salt out of the trailer after each use, the damage may already be extensive.