I've done some work offshore using air pressurizing/ purging on both control cabinets and electrical motors. These applications are used for classified areas but could be applied in this instance. By bring a good supply of air and pressurizing your motor you could avoid the caustic salt air...
I've been using the Siemens DC contactors for Dynamic Breaking circuits. They haven't failed me yet. The coil voltages you use are different but they do have them available for your application and they are a more rugid Nema design. Hope this helps.